BAGHDAD - The U.S. and Iraqi militaries have tentatively agreed to keep a joint base on the edge of Baghdad's Shiite slum of Sadr City, maintaining an American presence in a strategic area even after the June 30 deadline for U.S. combat troops to pull out of the capital.

The base -- Joint Security Station Commanche -- is one of about 14 joint facilities that U.S. officials say privately that they would like to keep in flashpoint neighbourhoods after the deadline.

Commanche is the most significant because it controls the area where Shiite militants poured rocket fire onto the Green Zone during the last major fighting in the city in 2008. Militants are believed to be trying to regroup in the area.

"We consider that critical," Brig.-Gen. Mike Murray, a deputy commander of U.S. forces in Baghdad, told The Associated Press on Tuesday.

But keeping the base after the end of the month would require the approval of the Iraqi government, which is under pressure to show its supporters the United States is sticking to the withdrawal schedule laid down in the U.S.-Iraq security agreement.

The pact, which took effect Jan. 1, specifies that combat troops must withdraw, not necessarily advisers and trainers working alongside Iraqi forces.

The plan to maintain a few joint bases reflects an attempt to meet the overall goal of the withdrawal plan without giving Shiite and Sunni extremists an opportunity to regain a foothold in parts of the city as the Iraqis assume more responsibility.

The status of the troops left behind in Baghdad has been kept vague, probably to avoid embarrassing the Iraqi government, which has told its people that all combat forces will be out on time.

Regardless of their formal status, all U.S. troops in Iraq are armed and trained to fight. U.S. officials have declined to say how many troops would stay behind under their plan.

A series of deadly bombings in April and May cast doubt on Iraqi capability to maintain security and raised fears of a resurgence in violence after the Americans withdraw. Seven people were killed and 28 wounded when a bomb exploded Wednesday night in a tea shop in west Baghdad, police said.

Iraqi government officials could not immediately be reached for comment on the plan to keep the joint base on the edge of Sadr City. But Firyad Rawndouzi, a member of the parliament's security and defence committee, said some "unstable areas" may require "U.S. support" after June 30.

"But such operations must be co-ordinated and approved by the Iraqi government and the Iraqi commanders," Rawndouzi said.

Keeping any U.S. troops in Baghdad is likely to draw criticism that the Americans are failing to live up to their commitment to leave the country by the end of 2011 as stated in the deal.

Followers of anti-American Shiite cleric Muqtada al-Sadr opposed the security agreement when it was approved last year, saying it had loopholes for the United States to avoid the withdrawal timetable.

Sadrist legislator Baha al-Aaraji said "the coming days will prove our reading of the agreement" that the "occupation forces will not withdraw from Baghdad" as well as Mosul and Diyala provinces, where insurgents remain active.

Murray said he believes insurgents will use the period after June 30 to test the capabilities of the Iraqi security forces in Baghdad.

"I expect violence to increase so they can make claims they chased us out of the cities," he said as U.S. troops tore down blast walls and prepared to hand over another joint security station in eastern Baghdad.

Another joint U.S.-Iraqi base on the edge of Sadr City will be closed later this month, Murray said.