The attack near the disputed city of Kirkuk came as Iraqi Prime Minister Nouri al-Maliki insisted that the Americans will withdraw on schedule.
Worshippers were leaving the mosque in the Taza area following noon prayers when the truck exploded, according to police Brig. Gen. Sarhat Qader.
He said at least eight houses were demolished and residents were working with rescue teams to search for people buried under the rubble.
Tensions have risen in the oil-rich area of Kirkuk as Kurds seek to incorporate it into their semiautonomous region despite opposition from Arabs, Turkomen and other rival ethnic groups. That has raised concerns about an outbreak of ethnic violence in northern Iraq even as attacks elsewhere decline.
U.S. and Iraqi officials have warned they expect insurgents to stage attacks to try to provoke a new outbreak of sectarian violence and undermine confidence in the government's ability to protect its people.
A U.S.-Iraqi security pact requires the Americans to pull back combat troops from cities by the end of this month as a first step toward a full withdrawal by 2012. The deal includes a provision for the Iraqi government to ask for U.S. help if violence surges.
Prime Minister Nouri al-Maliki insisted earlier Saturday that the withdrawal will take place on schedule, saying it will be a "big victory" for the nation.
He acknowledged that more attacks were likely but said Iraqi security forces were prepared to deal with it.
Any extension would show a lack of confidence and would be a "historic setback," he said during a speech to members of the Turkomen ethnic minority.
