BAGHDAD (AP) - Four U.S. soldiers were killed in combat shortly before the American military completed a withdrawal from Iraq's cities, and the prime minister assured Iraqis that government forces taking control of urban areas on Tuesday were more than capable of protecting the country.

Nouri al-Maliki said in a televised address that "those who think that Iraqis are not able to protect their country and that the withdrawal of foreign forces will create a security vacuum are committing a big mistake."

The streets of Baghdad were relatively quiet, as the Iraqi government named June 30 National Sovereignty Day and declared it a public holiday.

In the walled-off Green Zone in central Baghdad, al-Maliki and other Iraqi leaders appeared at a military parade to mark the day.

Iraqi infantry soldiers wearing khaki uniforms and policemen in blue uniforms marched in formation near the Tomb of the Unknown Soldier while Iraqi helicopters flew overhead. U.S.- and Russian-made tanks also drove by along with blue-and-white Iraqi Humvees.

The withdrawal that was completed on Monday was part of a U.S.-Iraqi security pact and marks the first major step toward withdrawing all American forces from the country by Dec. 31, 2011. President Barack Obama has said all combat troops will be gone by the end of August 2010.

In the attack Monday against U.S. forces, the military said the four soldiers who were killed served with the Multi-National Division-Baghdad but did not provide further details pending notification of their families. It said they died as a "result of combat related injuries."

It was the deadliest attack against U.S. forces since May 21, when three soldiers were killed and nine others were wounded in a roadside bombing in southern Baghdad.

The top U.S. commander in Iraq said the latest deaths show militants remain a threat but said he was confident Iraqi security forces could face the challenge.

"It reminds me that there are still dangers out there. There are still people out there who do not want the government of Iraq to succeed. They do not want to see a democratic country move forward," Gen. Ray Odierno said Tuesday at a news conference.

He said many of the attacks in Baghdad were being carried out by militants being funded or trained by Iran, including powerful roadside bombs and rocket strikes against the Green Zone, which houses the U.S. Embassy.

But, he said, the number of such attacks was "significantly smaller" due to security measures making them more difficult to carry out.

"Iran is still supporting, funding and training surrogates who operate inside of Iraq. They have not stopped and I don't think they will stop," Odierno told reporters at Camp Victory, a U.S. military base on the western edge of Baghdad.

He also said that 130,000 U.S. troops remain in Iraq, although he declined to say how many would remain in cities as trainers and advisers.

"We will be here, we are not leaving," he said. "We'll continue to be in support of the Iraqi security forces to maintain and improve stability throughout the country and I feel confident that we'll be able to do that."