For months, U.S. officials have warned that the insurgency in Iraq would grow deadliest as the June 30 political transition drew near. Now, they're warning the violence might get even worse once the handover is completed.

And that could mean the need for more U.S. troops, the commander of U.S. forces in the Middle East says.

President Bush on Wednesday acknowledged that Iraq could remain dangerous and unstable after the transfer of political power.

"It's tough work there now because killers want to stop progress," the president said following an Oval Office meeting with Silvio Berlusconi (search), premier of Italy, a strong ally in the war. "It will be tough work after sovereignty is transferred because there will still be people there trying to derail the election progress."

Earlier, testifying before a Senate panel, Gen. John Abizaid (search) predicted that the violence likely would continue — and perhaps get worse in the second half of the year when a yet-to-be-named Iraqi interim government will be put in charge.

"It could very well be more violent than we are seeing today, so it's possible that we might need more forces," Abizaid said, adding that he hoped more countries would contribute troops.

There now are about 155,000 coalition troops in Iraq, of which about 135,000 are American.

The Army is struggling to find enough forces to maintain the 135,000 level, so if Abizaid decides even more are needed, the strain would be enormous.

Bush administration officials had stuck for months to the publicly expressed hope that June 30 would be a turning point, not just in terms of moving Iraq toward democracy but also in improving security.

The insurgents were stepping up attacks, officials often said, because they believed that their best hope for chasing out U.S. forces was in the period before June 30.

The insurgency began to intensify in late March, highlighted by the killing and mutilation of four American private security contractors in the city of Fallujah on March 31. In April, more than 130 U.S. troops died — by far the highest monthly death toll since U.S. forces invaded in April 2003. So far this month, at least 47 additional troops have died.

Earlier this month, Defense Secretary Donald H. Rumsfeld (search) first mentioned the possibility that the violence would continue, or even grow worse after June.

"So you're going to have a period of uncertainty from now, and you're also going to have a period of increased attacks," he told reporters on May 4. "I mean, we just have to expect that. There are people who don't want this to happen in that country. And they are going to conduct attacks in that country against coalition, against Iraqis, against the United States."

Rumsfeld said it was inevitable that the violence would last at least until December.

In his remarks Wednesday, Abizaid said that although he is satisfied with the number of combat troops and armored vehicles available in Iraq, he is "not comfortable" with the support structure for them.

"There are certain types of troops that we don't have enough of and we still don't have enough of them and we got to figure out how to get them," he said.

He mentioned as examples the military police, military intelligence and civil affairs troops who are key to stabilizing a broken country like Iraq.

Abizaid said this was not a matter of the Pentagon refusing to provide the support forces. They simply don't exist in sufficient numbers in any part of the military — active duty or reserves.