With his strongest ally, embattled British Prime Minister Tony Blair, by his side, President Bush admitted Thursday that his "tough talk" in the early days of the Iraq war was probably a mistake.

The uncharacteristic mea culpa from Bush was in reference to his 2003 comments to the then-budding Iraqi insurgents to "bring it on" and his post-September 11, 2001 comments that he wanted terror leader Osama bin Laden "dead or alive."

"Kind of tough talk, you know, that sent the wrong signal to people," Bush said. "I learned some lessons about expressing myself, maybe in a more sophisticated manner. ... I think in certain parts of the world it was misinterpreted." Worse than his ineloquent comments, though, Bush said, were the abuses of Iraqi prisoners by American guards at Abu Ghraib prison, which he termed the "biggest mistake that's happened so far."

However, news broke just before the press conference about a military investigation that is expected to blame a group of Marines for the murder of two dozen Iraqi civilians on November 19. According to the Los Angeles Times, sources said the investigation could result in charges of murder, elevating the incident to one of the most serious cases of misconduct by American forces in Iraq.

Officials told the paper that preliminary results of the inquiry found that civilians in the insurgent stronghold of Haditha did not die from an improvised explosive device, as the military first reported, or in cross-fire between Marines and insurgents, as was later claimed.

The evidence points to a group of about a dozen Marines carrying out a three- to five-hour sweep in which civilian men, women and children were shot after a roadside bomb killed their fellow Marine, Lance Corporal Miguel Terrazas; a separate inquiry has been launched to investigate whether the incident was deliberately covered up.

According to the investigation, after the bomb killed Terrazas, the Marines conducted a routine sweep of the area, killing several Iraqis in homes as well as five who had been sitting in a vehicle, reportedly without provocation.

A spokesperson told the Times that the battalion commander and two company commanders from the division were relieved of duty last month because of a loss of confidence in their leadership.

Although both Bush and Blair are facing all-time low approval ratings at home -- with Blair dipping a few points below Bush's 29 percent, according to recent polls -- they stood firm in their commitment to staying the course in Iraq.

"I understand what it means to have troops in harm's way, and I know there's a lot of families making huge sacrifices here in America," Bush said during the rare evening news conference. "But I also understand that it is vital that we do the job, that we complete the mission."

Blair is in Washington to report to Bush on his recent meetings with Iraq's new prime minister, Nouri al-Maliki, who suggested to Blair that Iraq could be ready to take on full control of its security by the end of next year. While Blair said he left the meeting feeling that the challenge in Iraq is still "immense," he also felt "more certain than ever that we should rise to it.'' Bush dismissed as press speculation reports that the Pentagon could reduce troop levels from 131,000 to 100,000 by the end of 2006.

Neither man, however, said that the war itself was a mistake, nor would they concede that the failure to find WMD's was a critical one.

"We did not find the weapons of mass destruction that we all believed were there, and that's raised questions about whether the sacrifice in Iraq has been worth it,'' Bush said. "Despite setbacks and missteps, I strongly believe we did and are doing the right thing."