A suicide attacker using a bomb-laden lorry has killed 14 people at an Iraqi army checkpoint in the city of Tal Afar, a medical source told the BBC.
Gun and bomb attacks are a part of everyday life in Iraq
Four soldiers and 10 civilians died in the blast in the northern city which US President George W Bush held up as a model in a speech in March.
The renewed violence comes as it appears the US may be considering a major change in policy on Iraq.
Reports of a change came after a visit to Iraq by a senior Republican senator.
Tal Afar, to the west of Mosul, was supposed to be a showcase for American-led efforts to pacify Iraq, the BBC's Jim Muir reports from Baghdad.
Earlier this year, Mr Bush spoke at length about the city which he said had been effectively liberated from al-Qaeda control.
Also in the north, the important oil city of Kirkuk has been placed under total curfew as thousands of members of the Iraqi security forces backed by US-led coalition troops comb it for insurgents.
Iraqi police sources say a trench 15km (eight miles) long and two metres deep has been dug around part of the city in a bid to control access.
Senator John Warner, chairman of the Senate armed services committee, offered a bleak assessment of the situation and talked of the need for new options to be considered when he returned from a recent visit to Iraq.
He suggested that events there were drifting and that the time was coming for bold decisions to be made.
"In two or three months, if this thing hasn't come to fruition and if this level of violence is not under control and this government able to function, I think it's the responsibility of our government, internally, to determine: is there a change of course that we should take?" he said.
Sen Warner's comments are anything but routine, the BBC's Justin Webb reports.
While he did not specify what the decisions might be it is being suggested that he might have been preparing the ground for the White House to give up waiting for Iraqi Prime Minister Prime Minister Nouri Maliki to establish order.
That is a decision which could lead to a timetable for the return of US troops or an acceptance that a single Iraqi nation is no longer viable, our correspondent says.
Larry Diamond, a former adviser to the Coalition Provisional Authority in Baghdad, told the BBC on Saturday that the US had two options - either stay the course or leave gradually in the hope of shocking the Iraqi government into stabilising the country.
"There's no prospect that Iraq in the near term is going to become a reliable and democratic ally of the West," he told the Today programme.
"The only question is whether Iraq can be stabilised and prevented from descending into all-out civil war and whether western Iraq can be prevented from becoming what it is in the process of becoming - and what Afghanistan was before 11 September - a haven and training ground for terrorist attacks against the West."
In another development, US officials said that about 4,000 Iraqi policemen had been killed performing their duties over the past two years, with another 8,000 injured.