Several major explosions were heard in Baghdad Sunday morning in the vicinity of one of Saddam Hussein's main presidential compounds. Reporters also say helicopters were active in deploying U.S. troops at several locations in the city.

In central Baghdad, U.S. Marines exchanged heavy fire Saturday evening with Saddam Hussein loyalists. Troops also discovered large Iraqi arms caches near homes and schools in densely populated parts of the city.

VOA correspondent Alisha Ryu on the outskirts of the city said U.S. military officials believe the arms might have belonged to Saddam Hussein's elite troops, the Republican Guards. "They were located outside of Baghdad, but what happened was that as the Republican Guard units started falling, they took a lot of those weapons and moved them into the city, possibly for street-to-street fighting that never occurred, [or] possibly because the collapse of Iraqi command and control capabilities happened so quickly that they were not able to mobilize a lot of this stuff," she said.

Elsewhere, the U.S. Central Command says a man carrying a Syrian passport shot and killed an American Marine guarding a medical facility in Baghdad Saturday.

Syria, meanwhile, is accusing the United States of trying to destroy Iraqi institutions, and is again denying U.S. accusations that it has sought to help Iraqi troops loyal to Saddam Hussein.

In the oil producing region of northern Iraq, Kurdish forces that seized the city of Kirkuk on Thursday say they are turning control over to U.S. troops, who are securing the oil fields and airport.

Combat attention is focused now on Saddam Hussein's hometown of Tikrit north of Baghdad, the only major city coalition forces have not taken. An American television network broadcast pictures from an abandoned Iraqi military base on the outskirts of the city. The CNN reporter on the scene said some of the tanks and armored personnel carriers seemed derelict and some of it looked as though it had been recently abandoned.

The crew tried to enter the city but came under fire from Saddam loyalists forcing it to withdraw.

American soldiers are reported to be approaching the city, which bombers have been pounding in advance of an attack while the 10,000 strong U.S. 4th Infantry Division is moving into Iraq from Kuwait.

Relief organizations, meanwhile, say the security situation in Baghdad and other Iraqi cities is catastrophic and preventing the widespread delivery of aid. The International Committee of the Red Cross says only three of Baghdad's more than 30 hospitals remain open.

U.S. forces have opened two key bridges across the Tigris River. But looters took advantage of the opening to pillage new areas of the capital. VOA's Laurie Kassman in Baghdad said the destruction is widespread. "There were government buildings, especially, that were on fire, or had already been destroyed. In fact, we passed by the Air Force headquarters, and that was still on fire. There were plumes of black smoke coming up from buildings that had been, obviously, destroyed and ransacked," she said.

The United States is sending 1,200 political and judicial experts to Iraq to help restore order.

U.S. command spokesman Vince Brooks said the looting is tapering off. He notes that the situation is better elsewhere, such as Mosul in the north, where U.S. forces have entered after its fall Friday to Iraqi Kurdish fighters. There, looting has diminished and local leaders have established civilian patrols. "This is occurring in other places as well and we see stability occurring in more and more places throughout the country," he said. "There are many more issues to be dealt with in Baghdad particularly one, because of its size, and secondly, because of the intense pressure that the regime had in that city."

The Red Cross and Human Rights Watch say the United States is a temporary occupying power under international law, and therefore is obligated to ensure the safety of the civilian population under its control. Saddam Hussein's scientific advisor has surrendered to U.S. forces in Baghdad, becoming the first of 55 wanted members of the Iraqi regime to do so. General Amir al-Saadi turned himself in Saturday. He told German television, which filmed his surrender, that Iraq does not have nuclear, chemical or biological weapons.