Despite protests around the world and criticism at home, President Bush marked the third anniversary of the military invasion of Iraq by expressing confidence in Iraqis to form a unity government and thanking the U.S. military for its service.

"Today, my reflections are upon the sacrifices of the men and women who wear our uniform. ... They volunteer — many volunteered after 9/11 knowing full well that their time in the military could put them in harm's way. I think that all Americans should offer thanks to the men and women who wear the uniform and to their families who support them.

"May God continue to bless our troops in harm's way," he added.

Bush also said that he had spoken earlier in the day with U.S. Ambassador to Iraq Zalmay Khalilzad, who said he is "encouraged" by efforts of the Parliament elected in December to put a unity government in place.

"The Iraqi leaders are working together to enact a government that reflects the will of the people, so I am encouraged by the progress, the ambassador was encouraged by it," Bush said. "I encourage the Iraqi leaders to continue to work hard to get this Iraqi government up and running."

Elsewhere in Washington, D.C., Vice President Dick Cheney said that Iraq is not in the midst of a civil war, and violence on the ground is a desperate tactic by terrorists to prevent democratic progress.

"What we've seen is a serious effort by them to foment a civil war," Cheney said in an interview on a network news show. "But I don't think they've been successful."

Nonetheless, the top commander of multinational forces in Iraq said he expects the United States to remain there for at least the next few years.

"I see a couple of more years of this with a gradually reducing coalition presence here in Iraq ... as the Iraqi security forces step forward," Gen. George W. Casey told a Sunday network news show.

Casey said he did not think at the time the war began that the insurgency in Iraq would be as robust as it has been. He told "FOX News Sunday" that the Iraqis are making significant progress in building their new government, rebuilding their economy and securing their homeland. With each accomplishment, the day draws nearer when U.S. troops will come home, he said.

But positive reports of progress haven't silenced critics, who say the administration's strategy for waging the war and insuring the peace was built on deception and attempts to mislead Americans on the situation on the ground.

"They misled us into believing there were weapons of mass destruction and connections between 9/11 and Saddam Hussein. None of that existed," Sen. Dick Durbin, D-Ill., told "FOX News Sunday."

"They did not provide the necessary troops, the necessary equipment and the necessary leadership at a time when we need it. We've lost over 2,300 of our bravest and best Americans to date. ... Even our own ambassador is acknowledging the fact that we've opened Pandora's Box and the leaders have said in Iraq that we're facing nothing short of civil war. Here we are, on the third anniversary, with no end in sight," said Durbin, the second ranking Democrat in the U.S. Senate.

Many of the administration's most vocal critics are demanding that U.S. troops be withdrawn.

"I think you'll see a substantial withdrawal this year. They are trying to lay the groundwork for that, they are trying to put the onus on the military, and of course, they are trying to find a way to say that things are getting better so we can deploy our troops or withdraw our troops," said Rep. Jack Murtha, D-Pa., who has called for immediate redeployment of U.S. soldiers to neighboring nations.

"This is President Bush's war. He went into his war against the advice of his dad, against the advice of many military commanders. He went in with inadequate forces for the transition to peace, he didn't have an exit strategy," said Murtha, adding that he thinks the war will be a big issue in the congressional midterm election in November.

But in an editorial in The Washington Post, Secretary of Defense Donald Rumsfeld disagreed with critics who want an immediate withdrawal.

"Consider that if we retreat now, there is every reason to believe Saddamists and terrorists will fill the vacuum — and the free world might not have the will to face them again. Turning our backs on postwar Iraq today would be the modern equivalent of handing postwar Germany back to the Nazis," Rumsfeld wrote.

Rumsfeld added that Iraqis want the coalition to succeed, they want a better future for themselves and they are risking their lives to achieve it. This, he wrote, is what's important to remember on the third anniversary of Operation Iraqi Freedom.

But weeks of sectarian violence has some lawmakers suggesting that Iraq is descending into unending violence, and that sentiment was bolstered Sunday by Iraq's former interim prime minister Ayad Allawi, who claims Iraq is already in a civil war.

"It is unfortunate that we are in civil war. We are losing each day at an average 50 to 60 people throughout the country, if not more. If this is not civil war, then God knows what civil war is," Allawi told the British Broadcasting Network.

Some Democrats say America's first obligation is to protect U.S. forces by not allowing them to get caught up in a civil war.

"The message should be clear to the governments in the region and to the American people that our forces are coming out. It's the responsibility of the Iraqis to meet our schedule not the United States to meet their schedule," said Sen. Jack Reed, D-R.I.

In separate responses, Cheney and Casey both disagreed with Allawi, saying the perception of violence is enhanced by media reports that detail only the bad news of the day. Casey said violence is in fact isolated, and much progress is being made throughout the country

"I will tell you the violence in Iraq is not necessarily widespread. There is sectarian tension and there is sectarian violence, but it's primarily focused in the center of the country around Baghdad. In 15 of the 18 provinces, there are six or less incidents of violence a day. That's not just sectarian. That's all kinds of violence. In 12 of the provinces, it's two or less incidents of violence a day. So the country is not awash in sectarian violence," Casey said.

"There is a constant sort of perception, if you will, that's created because what's newsworthy in the car bomb in Baghdad," said Cheney. "It's not all the work that went on that day in 15 other provinces."

Cheney added that he did not think optimistic statements that he has made about the war have contributed to Americans' skepticism about it. The vice president said statements he made 10 months ago that the insurgency was in its last throes "were basically accurate, reflect reality."

On Sunday, Iraqi police were increasing security around the Shiite city of Karbala to preempt any more attacks from taking place there. Already, one mortar round exploded in a crowd there on Sunday, but did not cause casualties.

The city is the site of a major religious holiday on Monday and is expected to welcome 2 million pilgrims to the city. The Imam Hussein shrine, where one of the festivals is taking place, is one of the four holiest Shiite sites in Iraq, rivaling the Golden Mosque in Samarra, which was destroyed last month, sparking much of the recent sectarian violence.

In addition, last week, the U.S. military launched its largest operation since a month after the war began in March 2003. Operation Swarmer has resulted in the discovery of 11 caches of weapons and the detention of 80 suspected insurgents, the U.S. military press center reported Sunday.

Casey acknowledged that the situation on the ground is fragile in Iraq, and will remain so until a new national unity government is formed. But citing training of Iraqi security forces and elections over the past year, Casey added that good progress was being made politically and militarily in Iraq.

"What the long-term nature of our presence here might be is a subject for a discussion with the new government of Iraq," he said.

FOX News' Kelly Wright, Andrew Stack and Sharon Kehnemui Liss and The Associated Press contributed to this report.