A truck bomb killed at least 63 people Saturday as they were leaving a mosque near the contested northern city of Kirkuk, shattering a recent lull in violence and raising fears of renewed bloodshed as U.S. forces complete their withdrawal from Iraqi cities by the end of the month. The bombing came shortly after Prime Minister Nouri al-Maliki urged a gathering in Baghdad to remain steadfast if the American withdrawal led to a resurgence in attacks. 'I and you are sure that many don't want us to succeed and celebrate this victory,' he said. 'They are getting themselves ready to move in the dark to destabilize the situation, but we will be ready for them, God willing.' Also Saturday, the British government said two bodies believed to be those of Britons taken hostage in 2007 were handed over to British officials in Iraq. The fate of three others seized with them remains unknown. The hostages, computer consultant Peter Moore and his four bodyguards, were kidnapped by a Shiite militant group at a Finance Ministry building in Baghdad in May 2007. British Foreign Secretary David Miliband said the bodies had not been formally identified. In the attack Saturday, a suicide bomber detonated a truck loaded with explosives as Shiite Muslim worshipers left the mosque after noon prayers in the northern town of Taza, 14 miles south of Kirkuk. The dead included women and children, officials said, and more than 170 people were wounded. The explosion caused the mosque and at least a dozen mud houses to collapse, security officials said, and many victims were feared trapped under the rubble. Soon after the blast, police and medics rushed to the scene as bystanders ferried the dead and wounded to Kirkuk's main hospital. Iraqi police and security forces cordoned off the area, as U.S. soldiers collected evidence from what remained of the truck. Relatives dug graves in the cemetery behind the mosque for their loved ones. By nightfall, Iraqi and American rescue teams had set up lights as they continued to search for people buried under the debris. 'All I could see was a fireball flying into the air followed by a thick cloud of dust and smoke,' said Qanbar Abdullah Sajjad, 38, who owns a vegetable store a few steps from the bombing site. 'People were bleeding and shouting for help.' The majority of residents in the area are Shiite Muslims from the ethnic Turkmen community. Kirkuk, which sits over vast oil reserves, is in one of Iraq's most combustible regions, contested by Kurds, Turkmens and Arabs. Many of Taza's residents were refugees in neighboring Iran and came back to their town after the U.S.-led invasion of Iraq toppled Saddam Hussein in 2003. They are believed to be strong supporters of Maliki and his Dawa party. 'Why would they attack us? We have done nothing wrong to anyone,' said Mujtabi Tazaly, 49, who was sobbing outside his collapsed house, where his wife and children were still buried. Tensions have recently increased in Kirkuk, as Kurds seek to incorporate it in the Kurdistan Regional Government. But Arabs, Turkmens and other ethnic groups are strongly opposed to that. Security forces loyal to the Kurdish regional government and those who take orders from leaders in Baghdad have a history of distrust and animosity in Kirkuk and other disputed areas. U.S. and Iraqi officials have said they fear that insurgents will exploit those fissures as U.S. forces draw down in coming months. A string of devastating explosions in Baghdad in April and other recent attacks have led many to voice doubts about the ability of the Iraqi forces to control security after the Americans pull back. Under a U.S.-Iraqi security agreement, all American combat troops must withdraw from cities by June 30 and from Iraq by the end of 2011. Mohammad Takki Mufti, a 60-year-old farmer who lost four relatives in the explosion, accused the Sunni insurgent group al-Qaida in Iraq of carrying out the attack. 'Al-Qaida attacked us to sabotage the American withdrawal,' he said. 'We're paying for our land with our blood,' added Abdel Rahman al-Hussein, 45, a garbage man, standing near him at the scene. Correspondent Ernesto Londono in Baghdad and a special correspondent in Kirkuk contributed to this report. 