Pentagon Press Secretary Geoff Morrell says the U.S. military is expecting an increase in violence in Iraq as next week's deadline approaches for all U.S. combat forces to withdraw from Iraqi cities. The spokesman's remarks came on the same day Iraqi officials say a bomb blast in Baghdad killed at least 72 people.

Morrell told reporters at the Pentagon that security incidents remain at an all-time low in Iraq since the U.S.-led invasion in 2003.

He says despite sporadic high-profile attacks, the overall security climate is good, but U.S. military commanders in Iraq are concerned about a potential spike in violence.

"I do believe that we have an expectation, based upon the pattern of behavior what we have seen over the past few weeks and frankly, historically in Iraq, leading up to seminal dates, whether it be elections or other significant dates, of an uptick in the operational tempo of terrorists and insurgents," said Geoff Morrell.

Morrell's remarks came as Iraqi officials say a bomb blast tore through a market in Baghdad's mostly Shiite neighborhood of Sadr City.

Earlier this week a series of attacks left dozens dead and last Saturday a truck bombing near Kirkuk killed dozens and wounded hundreds.

The violence comes as the June 30 deadline approaches for U.S. combat forces to pull out of Iraq's urban areas.

Morrell says there will be small numbers of U.S. soldiers that will stay behind in cities to act as advisors to the Iraqi military.

"We are going to have some complement, albeit in much smaller numbers, of troops still in some Iraqi cities and towns in an advisory and assistance role until such time that the ISF, the Iraqi Security Forces, have developed to the point that they no longer need us in that capacity," he said.

Morrell says U.S. troops will form what he called layers of defense outside urban areas and will conduct combat operations with Iraqi forces outside of cities and towns.

He says U.S. soldiers will continue to conduct counterterrorism operations and a residual force will stay behind in Iraq when all combat brigades leave the country by the end of August next year.

Morrell says the goal is to make sure extremists do not become a strategic threat to the government.

"We think we have beaten back al Qaida to the point where they are now conducting attacks that are basically propaganda campaigns in an attempt to make it look as though they are driving us out of Iraqi cities, when in fact the truth of the matter is that the work of our brave men and women in uniform over the past couple years has created a climate such that we can leave Iraqi cities," said Morrell. "And the Iraqi security forces have developed to the point where they are capable of taking over that responsibility."

Iraqi officials have also warned that al-Qaida in Iraq and other violent groups will try to take advantage of the U.S. pullback to launch new attacks.