BAGHDAD  A suicide truck bomb exploded in a volatile region of northern Iraq on Saturday, killing at least 68 people and wounding nearly 200 more, even as Prime Minister Nuri Kamal al-Maliki pledged that attacks like it would not stop or slow the withdrawal of American troops.

Also on Saturday, the British government said the bodies of two men, believed to be among five Britons kidnapped by Shiite militants in 2007, had been turned over to British authorities in Baghdad.

The truck bombing, the worst single attack this year in Iraq, occurred shortly after noon prayers in a residential neighborhood near a mosque in Taza, a town south of Kirkuk, the capital of an oil-rich region that lies on the tense ethnic fault line between Iraq’s Arabs and Kurds, according to officials and witnesses.

The force of the blast gouged a crater in the ground and badly damaged dozens of homes, burying victims in the rubble, people and officials at the scene said, expressing fear that the death toll would rise even more.