BAGHDAD, Iraq (AP) _ The top U.S. commander in Iraq said Thursday he needs more international forces to deal with potential security threats _ but he and Defense Secretary Donald H. Rumsfeld both emphasized that they do not see a need for more U.S. troops.

Their comments came a day after Washington began pushing a new U.N. resolution aimed at persuading more nations to contribute troops. On Thursday, Russia gave its first signal that it could send peacekeepers to Iraq, and Britain said it was considering whether to increase its force levels.

The U.S. commander, Lt. Gen. Ricardo Sanchez, said at a Baghdad news conference that ``if a militia or an internal conflict of some nature were to erupt ... that would be a challenge out there that I do not have sufficient forces for.''

Sanchez cited al-Qaida terrorists, Iranian fighters and clashes between ethnic and religious militias as potential security threats. ``There are security challenges that are looming in the future that will require additional forces, and those are issues that with the coalition, and with time, can be resolved,'' he said.

Sanchez said the coalition lacks sufficient troops to protect Iraq's porous borders or its thousands of miles of highways. Iraqi security forces are being trained to eventually patrol both, he said.

Sanchez said if a sudden conflict arose he would reassign forces to deal with it, but added the Army's existing missions could suffer as a result. However, he maintained that no more U.S. troops are needed.

``I have communicated very clearly to Central Command, who in turn communicates to Washington ... and to senior leadership that has come through here, that I do not need additional U.S. forces,'' Sanchez said. ``Clearly, I have also stated that if coalition forces were to be offered, we would gladly accept them.''

Also Thursday, Rumsfeld arrived in Baghdad to see conditions firsthand and to talk to military and civilian leaders of the U.S.-led occupation.

Shortly after landing at Baghdad International Airport, Rumsfeld shook hands with troops and briefly visited wounded soldiers in a hospital tent. He planned to meet later Thursday with L. Paul Bremer, the civilian administrator in Iraq.

Rumsfeld said military commanders do not see the need for more U.S. troops in Iraq, but said more Iraqis need to be trained to help provide security. U.S. officials are considering allowing enlisted soldiers and junior officers from the former Iraqi military to join the U.S.-trained Iraqi security forces, he said.

Training and equipping Iraqi security forces is better than sending more American troops because the Iraqis are not an occupying force, Rumsfeld said.

``Foreign troops are not normal. They're temporary,'' he said. ``Iraqi forces are normal. They are what ought to be.''

In Russia, meanwhile, Defense Minister Sergei Ivanov gave the first signal that the Russians may send peacekeepers. ``It all depends on a specific resolution. I wouldn't exclude it outright,'' Ivanov said, according to the Interfax news agency.

And in London, Britain's defense secretary Geoff Hoon ordered a review of British troop levels following weeks of heightened insecurity. But Prime Minister Tony Blair said no decision had been made to send additional forces.

``We keep it under review constantly because we've got to get the job done, but there are no decisions that have been taken on additional troops,'' Blair said at a news conference.

Britain has 11,000 troops in Iraq. Forty-nine British soldiers have died in the war, with 11 of them killed since May 1 when President Bush declared an end to major fighting.

On Wednesday, the United States asked the United Nations to take an expanded role in Iraq's security, political transition and reconstruction. The draft resolution would transform the U.S.-led military force in Iraq into a U.N.-authorized multinational force under a unified command.

Amid the rhetoric over troop levels, new fighting erupted Thursday. U.S. forces exchanged fire with Iraqi guerrillas who lobbed at least six mortar rounds at them in intense fighting in downtown Tikrit.

The mortar shells missed their targets, causing no injuries or damage, said Lt. Col. Steve Russell. Russell commands the 4th Infantry Division's 1st Battalion, 22nd Regiment, which patrols Saddam Hussein's hometown of Tikrit, 120 miles north of Baghdad.

An American reconnaissance patrol, responding to the mortar attack, was ambushed with small-arms fire and rocket-propelled grenades on the eastern bank of the Tigris River, directly opposite the 4th Infantry's sprawling headquarters in one of the ousted leader's former palaces.

Bradley fighting vehicles were called in as reinforcements, opening fire on the guerrillas as tracer bullets lit the night sky over Tikrit, which was plunged into darkness. An intense firefight ensued and at least one house was on fire. Helicopters were heard hovering above.

Russell said no U.S. casualties were reported, but one attacker might have been killed as the rest of the guerrillas disappeared.

Elsewhere in Tikrit, U.S. troops acting on a tip from an Iraqi raided a house in Tikrit and detained four people, including a suspected bomb maker. The troops seized weapons and ammunition and a box of explosives, wires, clocks, nails and other bomb making material.

Also Thursday, Sanchez said U.S. troops would force the Badr Brigade, a Shiite Muslim militia, to disarm if reports of its reactivation prove true.

The Badr Brigade is the armed wing of the Supreme Council for the Islamic Revolution in Iraq. U.S. troops ordered the brigade disarmed and disbanded early in the occupation. But on Wednesday, Abdel-Aziz al-Hakim _ a member of the U.S.-picked Governing Council and brother of Ayatollah Mohammed Baqir al-Hakim, who was killed in last week's Najaf car bombing _ suggested the militia had rearmed to provide security for Shiites.