Syrian forces hit rebel areas of Damascus Syrian warplanes and artillery have pounded opposition strongholds in Damascus and its suburbs, as rebels in the northern city of Aleppo launched an operation to try to free hundreds of political detainees from the city's central prison. The fighting has escalated across Syria in recent weeks, particularly in Aleppo and Damascus, the country's largest cities, as the rebels and President Bashar al-Assad's regime try to gain the upper hand in the two-year-old conflict. The Britain-based Syrian Observatory for Human Rights said some 6000 people were killed nationwide in March alone, making it the deadliest month since the uprising began. Fighting has also intensified in the southern provinces of Daraa and Quneitra, across from Jordan and the frontier with Israel. On Tuesday, the Israeli military said a mortar shell exploded on its side of the frontier in the Golan Heights. The military said its soldiers returned the fire and recorded a direct hit. No other details were given. The incident came after Israeli Defence Minister Moshe Yaalon visited the region on Tuesday and warned that Israel would respond to any attack from Syria. The escalation in the southern Quneitra region along the ceasefire line separating Syria from the Israeli-occupied Golan Heights accented concerns that Islamic extremists among the rebel forces could take over the front line opposite Israeli troops. Damascus has become a key battleground in the civil war. From their strongholds in the suburbs, rebel fighters are trying to slowly push their way into the heart of the capital. Assad has deployed his most loyal and best equipped troops there, trying to insulate it from the violence. The Observatory said government forces on Tuesday shelled the northern Damascus neighbourhoods of Jobar, Barzeh and Qaboun. It also reported an air raid on the suburb of Mleiha. Maath al-Shami, an activist based in the suburb of eastern Ghouta, said there were several airstrikes in the area, which includes Mleiha. "Fighting is taking place on all fronts," he said, referring to clashes east of Damascus. "Drones fly over eastern Ghouta then warplanes come and bomb the area," al-Shami said, using his activist name because he feared government retribution. State-run TV said rebels fired a mortar shell on the Damascus suburb of Muqailabiyeh, killing four people, including two children. It claimed troops killed scores of gunmen throughout the country. The Observatory also reported that five people were killed, including a woman and an Iraqi national, when a barrage of mortar shells exploded in an area of the suburb of Jaramana, just few kilometres southeast of Damascus. The town is overwhelmingly pro-regime. In Aleppo, rebels launched an attack dubbed "Freeing the Prisoners" that aims to eventually free detainees held in the city's central prison, the Aleppo Media Centre activist group reported. Aleppo-based activist Mohammed Saeed said the operation is a three-pronged attack targeting at the Kindi Hospital, Ghondol square and the central prison. He said the hospital has been turned into a military compound recently. "The aim of the offensive is to strengthen the siege on the central prison and demand the release of political prisoners," Saeed said via Skype, adding that the goal is to free hundreds of political prisoners inside. He added that if the rebels manage to take the three areas, they can cut supply lines for government troops stationed in the city. Aleppo, Syria's largest city and a former commercial hub, has been a key battleground in the country's civil war since rebels launched an offensive there in July, seizing several districts before the fighting largely settled into a bloody stalemate that has left the city carved up into government- and rebel-held zones. In an attempt to combat rising crime and kidnapping for ransom as a result of the civil war, Assad issued a decree on Tuesday threatening life in prison at hard labour for any person who abducts someone for political or sectarian reasons or for ransom, the state news agency said. It said if the kidnapper kills, rapes or permanently disables the captive, then the abductor will receive the death sentence.