BAGHDAD, Iraq - Sunni Muslim Arabs will be given up to 25 seats on the committee drafting Iraq's new constitution, President Jalal Talabani said today.

The announcement, made during a visit to Baghdad by British Foreign Secretary Jack Straw, was a victory for Iraq's Sunni Arabs, who threatened to pull out of the political process if they were not given a bigger say on the committee.

"We have decided to add about 20 to 25 members from Sunnis in the committee, which will draft the constitution with full rights like other members who were elected by the parliament," Talabani said.

"This will be done very soon and we are discussing to finalize the making of this decision," he added.

Talabani's call seemed to meet demands made a day earlier by top Sunni leaders for 27 seats on a committee drafting the new constitution.

Two Sunni Arab lawmakers sit on a 55-member parliamentary committee drafting the charter, but Sunni Arabs felt this was too small a representation.

The Shiite-led government offered 13 extra places for Sunni Arabs from outside the parliament to help the 55-member committee draw up the constitution. No voting rights were offered to the 13, but the committee said it would make all decisions by consensus.

On Wednesday, however, Iraq's largest Sunni Arab organizations, the Iraqi Islamic Party and the Sunni Endowment, rejected the offer of 13, and instead demanded 25 seats with voting rights.

Sunni Arab support is crucial for Iraq's Shiite- and Kurdish-dominated government, particularly to approve the constitution. The draft charter will collapse if three of Iraq's four predominantly Sunni Arab provinces vote against it in a referendum later this year.

The constitution must be drafted by mid-August and approved two months later in a referendum. Sunni Arab approval is needed for the charter to take effect and new elections to be held in December.

Also today, the U.S. military said 16 private American security guards are under investigation for shooting at U.S. Marines and Iraqi civilians during a three-hour spree west of Baghdad.

The Marines said the 16 Americans and three Iraqi contractors were arrested and held in a military jail for three days after spraying small arms fire at Iraqi civilians and U.S. forces from their cars in Fallujah late last month. There were no casualties.

Many Iraqis resent high-profile security details who speed along highways in sports utility vehicles bristling with automatic weapons. Senior government officials, who are prime targets of militants wreaking havoc across Iraq, use private security firms for their own protection.

No charges have been filed yet following the May 28 shootings.

Marines spokesman Lt. Col. Dave Lapan said Marines reported seeing gunmen in several late-model trucks fire "near civilian cars" and on military positions.

"Three hours later, another Marine observation post was fired on by gunmen from vehicles matching the description of those involved in the earlier attack," Lapan said.

U.S. forces later detained the contractors without incident and held them for three days. The American contractors are thought to have left Iraq. A Naval Criminal Investigative Service inquiry is under way.

Separately, U.S. officials confirmed last week's arrest of Mullah Mahdi, Mosul cell leader of the feared Ansar al-Sunnah terror group, which has links to al-Qaida in Iraq..