Media playback is unsupported on your device Media caption The BBC's Jim Muir says unverified footage purports to show the aftermath of an attack on a funeral procession 
 
 Syrian troops have been mobilised in a drive to oust armed rebels from parts of Damascus, a day after a bomb attack that killed three top regime figures. 
 
 Tanks, artillery and helicopters have been deployed and clashes reported south-west and north-east of the city. 
 
 In a first public appearance since the bomb, President Assad was shown on TV swearing in the new defence minister. 
 
 Russia and China have vetoed a UN Security Council resolution calling for tougher sanctions on Syria. 
 
 Under the Western-backed plan, the Damascus government would have been threatened with non-military sanctions under Chapter 7 of the UN Charter if it failed to move troops and heavy weapons from populated areas. 
 
 It is the third time that Moscow and Beijing have vetoed sanctions against Syria. 
 
 With sporadic battles breaking out for control of Damascus, international envoy Kofi Annan has pushed the international community to take urgent and decisive action. 
 
 The Security Council must also decide whether to renew the mandate of a UN mission in Syria, due to end on Friday. 
 
 The whole city is shaken. Worried about passing any government building or checkpoint, people are choosing to stay at home instead Damascus-based reporter Damascus: 'City in grip of fear' 
 
 'Imminent fall' 
 
 The bombing at Syria's national security headquarters claimed the lives of three high profile figures in President Assad's defence establishment 
 
 Image caption The three men were at a security meeting at the time of the blast 
 
 Defence Minister and ex-chief of staff Gen Daoud Rajiha 
 
 Deputy Defence Minister Assef Shawkat, married to Mr Assad's sister Bushra 
 
 Assistant to the vice-president and head of crisis management office Gen Hassan Turkomani 
 
 Two other senior officials - interior minister Mohammad Ibrahim al-Shaar and National Security Bureau chief Hisham Ikhtiar- were wounded 
 
 Rebel groups said the bomb had been planted the day before the meeting at national security headquarters where it was detonated. They predicted the government's imminent fall. 
 
 In contrast with earlier explosions in Damascus, there were no photos or video from the scene. 
 
 After the attack the government vowed to root out ruthlessly what it described as armed terrorists backed by outside powers. 
 
 Media playback is unsupported on your device Media caption Unverified footage purportedly shows people celebrating following the death of the officials 
 
 Our correspondent says that video of one attack posted on the internet showed scenes of pandemonium after what activists said was a helicopter gunship attack on a funeral procession at Sitt Zeinab, south of the capital. They said at least 60 people were killed in this incident alone. 
 
 Activists also said there was fighting near the cabinet office on the western side of Damascus. 
 
 In the capital itself, state media said, security forces launched operations in many areas which have seen clashes in recent days, killing many "terrorists". 
 
 Activists reported more tanks moving towards the capital from the west. 
 
 But our correspondent says the rebels are on the offensive too, warning state TV and radio to evacuate staff before its headquarters comes under attack. 
 
 The London-based Syrian Observatory for Human Rights said on Thursday that more than 150 people had died across the country on Wednesday, in one of the worst days of a 16-month revolt. 
 
 'Losing control' 
 
 The head of the UN monitoring mission, Gen Robert Mood, condemned the attack and said he had sent condolences to the victims' families. 
 
 "It pains me to say, but we are not on the track for peace in Syria and the escalation we have witnessed in Damascus over the past few days is a testimony to that," he said. 
 
 The US said the killings were a major blow to the regime. 
 
 "I think the incident today makes clear that Assad is losing control," White House spokesman Jay Carney told reporters. "All of our partners internationally need to come together to support a transition." 
 
 UK Prime Minister David Cameron said Mr Assad should step down and that it was "time for transition in the regime". 
 
 In Lebanon, Hezbollah leader Hassan Nasrallah condemned what he termed a targeted killing: "We are going to miss them and we offer our condolences to the Syrian leadership and the Syrian army." 
 
 Russia said some countries had incited the opposition rather than calming it down. ||||| At least 27 people have been killed and 97 others wounded in a pair of explosions in Damascus, the Syrian health minister has said. 
 
 State television blamed "terrorists" for the Saturday morning explosions and reported that vehicles packed with explosives had been used. The blasts targeted buildings belonging to a customs office and air force intelligence. 
 
 Most of the casualties were civilians, state television said. The channel broadcast interviews with Syrians who blamed the attack on the United States and Gulf nations, including Saudi Arabia and Qatar, who they said had sent terrorists. 
 
 The attacks come two days after the one-year anniversary of the start of the uprising against Syrian President Bashar al-Assad. 
 
 "I woke up to two massive explosions around 7:30 this morning - one was on Baghdad street less than a mile away from my home," a witness in Damascus told Al Jazeera. "Relatives closer to the explosion told me their windows were blown out and doors destroyed from the blast." 
 
 Bassma Kodmani, a Paris-based member of the opposition Syrian National Council, said she doubted the armed groups trying to bring Assad down by force have the capacity to carry out such attacks on security institutions in the capital. 
 
 "I don't think any of the opposition forces or the Free Syrian Army has the capacity to do such an operation to target these buildings because they are fortresses,'' she said. "They are very well guarded. There is no way anyone can penetrate them without having strong support and complicity from inside the security apparatus." 
 
 State-run news agency SANA said a third blast went off near a military bus at the Palestinian refugee camp Yarmouk in Damascus later in the day, killing the two suicide bombers. 
 
 No claim of responsibility 
 
 It was not the first time bombers have struck in Damascus, the heart of Assad's power base. There were three alleged suicide bombings in the capital between December and January, which the government blamed on al-Qaeda. 
 
 "A few weeks ago, we saw security buildings also come under attack [in Aleppo] and the government has been blaming what they are calling 'terrorist groups'," said Al Jazeera's Zeina Khodr, reporting from Beirut. 
 
 She said no one had claimed responsibility for Saturday's attacks but that the opposition has in the past blamed the government for "orchestrating" them to bolster its case against alleged terrorists. 
 
 "But we also have to remember that US officials have hinted in the past that they believe that al-Qaeda could be involved, could be taking advantage of the security vacuum in that country," Khodr said. 
 
 The spectre of al-Qaeda could make Syria's minority populations more nervous about the Sunni-led uprising against Assad, whose government has sought to rally Alawite, Christian and Shia communities to its side. 
 
 One of Saturday's blasts happened in al-Qassaa, a predominantly Christian area. 
 
 International condemnation 
 
 UN Secretary-General Ban Ki-moon condemned the bomb blasts and called for an immediate end to the violence. 
 
 "Mr Ban extended his sympathy and condolences to the families of the victims and the people of Syria," a statement from the secretary-general's office said. 
 
 Alain Juppe, the French foreign minister, said: "France condemns all acts of terrorism, which cannot be justified under any circumstances." 
 
 France has been at the forefront of calls for Assad to quit. 
 
 Mohammed Kamel Amr, Egypt's foreign minister, affirmed Cairo's "fixed position against terrorism in any form, regardless of the reasons behind it". 
 
 Meanwhile, the Local Co-ordination Committees (LCC), an opposition activist network, said 22 people were killed across the country on Saturday, including eight in the northwestern city of al-Raqqa where security forces reportedly opened fire on a funeral march. 
 
 Al-Raqqa saw a rare mass rally against Assad on Friday and activists said several people were killed by gunfire. 
 
 Clashes between the military and army defectors were also reported in the city on Saturday. The LCC said security forces had besieged the hospital that admitted most of the injured.
– Damascus has been rocked by bombings for the past two days, with at least two large blasts hitting Syria's military headquarters there this morning. The Free Syrian Army claimed responsibility for the attack, said to be the largest since July explosions killed President Bashar al-Assad's brother-in-law and other key aides; the BBC reports that Assad would have been able to hear today's explosions from his palace. Gunfire broke out afterward, and Maya Nasser, a TV correspondent for the Iranian Press TV, was shot dead by sniper fire during a live broadcast, report the New York Times and Press TV. Other government facilities were hit by bombs yesterday, proving the opposition can still get past government security, but the regime is downplaying the scope of the attacks while the opposition says many of Assad's forces have been killed. In other news from Syria: UN Secretary-General Ban Ki-moon called for international action at the General Assembly yesterday, calling the conflict "a regional calamity with global ramifications," the AP reports. Click for more from the General Assembly on Syria. Clashes have also been reported near Syria's border with Israel, leading the Israel Defense Forces to issue a statement declaring that "fire from Syria leaking into Israel will not be accepted."