"Anybody who wants to harm American troops will be found and brought to justice," Mr. Bush said at an impromptu news conference at the White House. "There are some who feel like if they attack us, we may decide to leave prematurely. They don't understand what they're talking about if that's the case."
Increasing attacks have killed more than 23 U.S. soldiers and wounded dozens more since Mr. Bush declared major combat over on May 1.
On Tuesday, assailants traveling in a vehicle in central Baghdad fired a rocket-propelled grenade at a U.S. military vehicle, wounding three soldiers. Another grenade slammed into a U.S. truck on a road south of Baghdad, injuring three soldiers, one of whom died at a field hospital overnight.
"There are some who feel like that, you know, the conditions are such that they can attack us there. My answer is bring them on," Mr. Bush said. "We got the force necessary to deal with the security situation."
In other developments:
A sweep by U.S. forces to clamp down on anti-American insurgents, dubbed Sidewinder, moved into its fourth day Wednesday. The U.S. Army conducted 25 raids and detained 25 suspects, a military statement said. No major fugitives of Saddam's regime were among them.
Anger at the U.S. troops was on display in Fallujah, 35 miles west of Baghdad, where an explosion at a mosque killed at least 10 people. Locals said U.S. warplanes bombed a cinderblock building in the mosque's courtyard. U.S. military officials denied bombing the site, and said the blast was likely caused by explosives stored in the building.
According to the Washington Post, if the U.S. account is true it would be strong proof of Islamic involvement in the recent violence. One of those killed in the blast was a cleric, Laith Khalil, who had railed against the U.S. presence.
In western Baghdad, U.S. troops shot and killed two people when their car didn't stop at a checkpoint Tuesday, witnesses said. A U.S. military spokesman said he had heard about the incident but could not confirm it.
Later, two civilians were shot and killed at another checkpoint, one by soldiers who feared he was an insurgent and another by a stray bullet, witnesses said.
"This is a difficult situation for our soldiers over there," said CBS News military analyst Mitchell Mitchell, a retired Army colonel. "They are not really trained to do this type of operation. They are trained to go out and fight and win wars and keep the peace with large forces, not to do the individual police actions that they are required to do right now."
Mitchell said the reconstruction efforts need to more extensively involve Iraqis in the process and must include thousands more troops — three or four times the current U.S. force of 150,000. The additional manpower should be a multinational effort, Mitchell said.
Mr. Bush said he would welcome assistance from other countries willing to send troops to help restore peace.
"Anybody who wants to help, we'll welcome," Mr. Bush said. "But we got plenty tough force there right now to make sure the situation is secure."
Military officials said Wednesday said some 1,800 Ukrainian troops will be deployed to Iraq by Sept. 1 to join a 15-nation, 9,000-man contingent that will take control of central Iraq between British and American sectors. A first group of about 250 Polish soldiers was heading to Iraq on Wednesday.
Mr. Bush also promised harsh justice for people who sabotage Iraqi infrastructure such as power lines.
"Those who blow up the electricity lines really aren't hurting America, they're hurting the Iraq citizens," Mr. Bush said. "Their own fellow citizens are being hurt. But we will deal with them harshly as well."