BAGHDAD, Iraq -- Iraqi security forces will not be ready to protect the country against insurgents by the June 30 handover of power, the top U.S. administrator said Sunday -- an assessment aimed at defending the continued heavy presence of U.S. troops here even after an Iraqi government takes over.

The unusually blunt comments from L. Paul Bremer came amid a weekend of new fighting that pushed the death toll for U.S. troops in April to 99, already the record for a single-month in Iraq and approaching the number killed during the invasion that toppled Saddam Hussein last year.

The military had always planned to remain after June 30, when the United States will hand over sovereignty to Iraq. In recent months coalition officials acknowledged the transfer of security will be significantly slower than hoped because Iraqi forces are not prepared.

But Bremer said the fighting across the country this month exposed the depth of the problems inside the security forces.

"Events of the past two weeks show that Iraq still faces security threats and needs outside help to deal with them. Early this month, the foes of democracy overran Iraqi police stations and seized public buildings in several parts of the country," he said. "Iraqi forces were unable to stop them."

"It is clear that Iraqi forces will not be able, on their own, to deal with these threats by June 30 when an Iraqi government assumes sovereignty," Bremer said in a statement issued by the U.S. coalition.

With U.S.-led forces fighting on two fronts and insurgent violence flaring elsewhere, at least 99 U.S. troops have been killed in combat since April 1. In the latest violence, five Marines and five soldiers were killed Saturday.

A total of 115 U.S. servicemembers were killed in combat from the start of the U.S.-led invasion in March 2003 until May 1, when President Bush declared major combat over. Until now, the single-month record for U.S. troops killed was 82, in November. Around 700 U.S. servicemen have died in Iraq.

Over the weekend, at least 40 Iraqis were killed, bringing the Iraqi death toll in April to more than 1,050.

Also Sunday, Spain's prime minister ordered the withdrawal of Spanish troops from Iraq as soon as possible, fulfilling a campaign promise made after terrorist bombings that al-Qaida militants said were reprisal for Spain's support of the war.

Iraq's defense minister -- Ali Allawi, a Shiite Muslim -- appointed by U.S. officials two weeks ago, announced his two top generals, a Sunni and a Kurd, establishing representatives of the country's three main communities in the senior defense positions.

The army's top general will be Gen. Babakir Zebari, who commanded Kurdish militiamen in the north for decades and fought alongside coalition troops during last year's invasion. The chief of staff will be Amer al-Hashimi, a Sunni and former general in the Iraqi infantry until he retired in 1997.

U.S. officials have been rebuilding the military from scratch, arranging the training of recruits and naming Allawi as its civilian head.

But the recent violence has shown the weaknesses and conflicted feelings of the armed forces. An army battalion refused to join the Marines in the siege of Fallujah, saying they did not intend to fight fellow Iraqis. During the Shiite militia uprising in the south, many police abandoned their stations, realizing they were badly outgunned or sympathizing with the militia's cause.

In Husaybah, near the Syrian border, insurgents ambushed a Marine patrol Saturday morning, sparking a battle throughout the day with up to 150 gunmen, Marine spokesman Lt. Eric Knapp said. Five Marines and up to 30 insurgents were killed, he said. Hospital officials said civilians were among the dead, as well as the town's police chief.

Fighting continued Sunday in three neighborhoods of Husaybah, which was sealed off by U.S. forces. It is located at the far end of Iraq's western Anbar province, a Sunni Muslim area that is also home to Fallujah and Ramadi, two guerrilla strongholds.

Three soldiers were killed Saturday when their 1st Armored Division convoy was ambushed near the southern city of Diwaniyah. Another died when a roadside bomb exploded near a convoy in Baghdad, and a soldier assigned to the Marines was killed in action in western Iraq, separate from the fighting by the Syrian border.

A soldier also died in a tank rollover, and another was electrocuted in an accident in the northern city of Samarra.

Rockets aimed at a military camp in western Baghdad hit a nearby civilian area, killing two Iraqi civilians. Two U.S. civilian contractors and a soldier also were wounded.

A day and a half of calm in the besieged city of Fallujah was broken Sunday when Marines battled gunmen around a mosque.

U.S. officials and Fallujah representatives reported progress in negotiations on Friday and Saturday to ease violence in the 16-day Marine siege, when gunfire in the city all but halted. Talks were to resume Monday.

On Sunday, however, insurgents in a building opened fire on a U.S. tank, which returned fire and destroyed the building, located next to a mosque, Knapp said. Gunmen also fired from the mosque minaret, he said.

Meanwhile, U.S. forces struggled to maintain control of Iraq's highways, closing key roads because of insurgent violence.

The military announced that the highway to Jordan was closed at Baghdad's western entrance. The main route north was closed for a 42-mile stretch outside the capital, and a 90-mile section of the main southern highway connecting Baghdad with Basra and Kuwait was shut down.

Guerrillas around Baghdad's outskirts have been targeting key military supply lines, forcing the military to rely more on aircraft to bring in supplies, though commanders say there are no serious shortages for any units.

The violence threatens to hamstring U.S. reconstruction efforts. More than 1,500 foreign engineers and building contractors have fled Iraq for fear of being abducted or killed, Iraqi Housing Minister Bayan Baqer said Sunday. Some 40 percent of the military's food, water and fuel supplies are delivered by private contractors.

U.S. Army convoys have added more armed escorts and have varied routes and travel times, said Col. James P. Chambers, commander of the Army's 13th Corps Support Command, which operates military supply convoys that crisscross Iraq.

In Kuwait, where the U.S. 3rd Army is in charge of moving goods in and out of Iraq, more cargo is traveling on aircraft, said Army spokesman Lt. Col. Robert Johnson.

"Some soldiers may experience some shortages. The whole country is still a very dangerous place," Johnson said.

Also Sunday, a British soldier was wounded in fighting in the southern city of Amarah, a spokesman said. A military vehicle was seen burning while Iraqis nearby chanted slogans in favor of radical Shiite cleric Muqtada al-Sadr.