U.S. forces are working their way back to Iraqi cities they circumvented in order to first reach strongholds of Saddam Hussein's regime, Defense Secretary Donald H. Rumsfeld said Tuesday.

They will destroy any remnants of the Republican Guard or other Iraqi forces and examine clues to the whereabouts of four missing U.S. service members, POWs from the 1991 war and hidden Scud missiles or other illegal weapons, he told a Pentagon news conference.

"We'll continue these efforts until Saddam Hussein's regime has been removed from every corner of Iraq," Rumsfeld said.

U.S. Marines now control Saddam's hometown of Tikrit after attacking it from the south, west and north and capturing a key Tigris River bridge in the center of the city about 90 miles north of Baghdad, he said.

Meanwhile, fighting ended in Qaim, a town near the Syrian border where Iraqi holdouts had been battling U.S. forces for about a week, military officials said Tuesday. American troops still were negotiating with local leaders for control of the town, discussing issues such as whether and when a curfew would be imposed and what forces would police the town, the officials said.

Marine Corps Gen. Peter Pace, vice chairman of the Joint Chiefs of Staff, said it was not possible to say how many U.S. troops must remain in Iraq to get the country back on its feet.

"We are just now beginning to assess the status of the country," Pace told CBS' Early Show.

"We need to go through, literally, city by city, section by section, determine how much of the infrastructure has been let to rot and decay over the last decades of the regime, see how much work needs to be done and then assess the security situation," Pace said.

The Pentagon raised the official U.S. death toll in the war to 121, of which 105 were killed in action and 16 were nonhostile deaths. Four Americans are missing, and none are listed as POWs.

Rumsfeld said a U.S.-led group charged with laying the foundation for a new civil administration, or interim authority, for Iraq will enter the Iraqi capital "once conditions on the ground permit."

He described the interim authority as a steppingstone to a new Iraqi government.

"This much is certain: It will be temporary; it will be large, involving Iraqis from all walks of life; and it will be open to participation by new leaders from across the country as they emerge from the shadow of Saddam Hussein's repression," he said.

In the meantime, some U.S. forces in Iraq are being sent home while others arrive either to add new capabilities or to replace departing troops, Rumsfeld said. He confirmed that one ground force in line to deploy to Iraq has been told instead to stay home.

He would not identify the unit but others said it was the Army's 1st Cavalry Division from Fort Hood, Texas.

The size of the U.S. force remaining in Iraq as a post-war security force will depend in part, Rumsfeld said, on how willing other countries are to contribute peacekeeping troops.

Rumsfeld also said that it would take a while to decide the future arrangement of American forces in various Persian Gulf countries, many of which hosted U.S. troops that fought in Iraq.

"We have not made final decisions with respect to the footprint of the United States in that part of the world and won't for some months," he said.

Rumsfeld asserted that the United States and its main Iraq war partner, Britain, were making good progress in collecting promises from other countries for peacekeeping contributions.

He said he discussed the matter Tuesday with his counterparts from Britain and Poland.

"We've had good luck, good fortune," he said without saying whether any countries agreed to send troops.

The purpose of this force, which Rumsfeld did not describe in terms of its size or makeup, is to ensure that "over a period of time we'll be able to have the kind of security environment that is safe and allows a country to fashion a new government and a new approach to how they want to live their lives."

The Associated Press contributed to this report.