The largest U.S. military base in Afghanistan has a new crew running operations: troops from the 101st Airborne Division.

The renowned paratrooper corps took over the reins from Marines Saturday at bunkers along the borders of the base set up at Kandahar's airport.

No fanfare or formal ceremony marked the military swap that has been in the works for several days.

Although more than a month has passed since the Marines set up the installation in the area that gave birth to the Taliban, the area remains dangerous.

But while Marines are moving out nonessential personnel, they will "retain the capacity for any missions that might pop up," said Marines spokesman 1st Lt. James Jarvis.

Sightings of armed men outside the perimeter are reported frequently by troops, and the base came under fire last week during the first flight of Al Qaeda and Taliban prisoners from a temporary detention facility to a high-security jail at Guantanamo Bay, Cuba.

A man claiming to have significant information about the Taliban showed up at the gate earlier in the week and he remained under interrogation Saturday, said Army spokesman Maj. Ignacio Perez. He declined to say if the man was being formally held or would be free to leave if he wished.

About 2,000 Marines were at the Kandahar base at the height of their deployment and military officials declined to say how many would remain as the Army takes over. Dispensing with base duties would free some Marines for quick deployment on other missions.

The United States raised the specter of renewed foreign meddling in Afghanistan on Friday, saying that Iran may be sending pro-Iranian Afghan fighters to destabilize the newly installed U.S.-backed government.

U.S. special envoy to Afghanistan Zalmay Khalilzad stopped short of directly accusing Iran of interference but cited unspecified reports that Afghan fighters and money were being sent from Iran into the extremely volatile country to build opposition to Prime Minister Hamid Karzai.

"All of those things would be regarded as interference," Khalilzad said in Kabul, the capital.

Earlier this month, President Bush warned Iran against harboring Al Qaeda fighters and trying to destabilize Afghanistan's new government. An Iranian Foreign Ministry spokesman rejected Bush's remarks as "baseless."

Iran's official Islamic Republic News Agency reported Saturday that Iran has reinstated visa requirements for Arabs from Persian Gulf nations to keep out Al Qaeda members.

Iran's U.N. ambassador, Hadi Nejad Hosseinian, said the measure was taken to "remove the possibility of Al Qaeda members' use of the Iranian soil to travel to other countries," the agency reported.

The United States is continuing to scour Afghanistan for clues to the whereabouts of Saudi exile Usama bin Laden, the head of the network Al Qaeda that the United States holds responsible for the Sept. 11 terrorist attacks.

"I honestly don't know where he is," said Gen. Tommy Franks, the war's commander, but vowed he would be found.

"The world is not a large enough place for him today," the general said Friday in the United States. "He may hide today, he may hide tomorrow, but the world is not large enough a place for him to hide."

Franks also echoed Khalilzad's comments about Iran.

"There has been a perception among several of the leaders inside Afghanistan that Iran has in some cases not been terribly helpful," Franks told reporters.

U.S. forces are continuing to work against pockets of Taliban and Al Qaeda resistance — about 10 of them at any given time, Franks said.

"We have found tanks, we have found armored personnel carriers. We have found thousands and thousands of rounds of ammunition," Franks said.

Despite their common Islamic faith, Iran fiercely opposed the former Taliban leadership. Since the Taliban collapsed last month, Iran, Pakistan, India and other countries in the region have been competing for influence among the various Afghan factions.

On his first trip abroad since taking office Dec. 22, Karzai met with Saudi Arabia's King Fahd on Saturday, discussing Saudi diplomatic recognition for his post-Taliban government and financial aid, Afghan diplomats said.

Saudi Arabia, which was one of just three countries that recognized the Taliban regime before it severed ties in September, is expected to recognize the new Afghan government and appoint an ambassador soon, Afghan diplomats said on condition of anonymity.

In talks Saturday with Crown Prince Abdullah, Karzai discussed the issue of Saudi citizens held in Afghanistan and the possibility of repatriating them for trial or for debriefing, the diplomats said.

Saudi officials have demanded that Saudi citizens who have been captured or have surrendered in Afghanistan be handed over to Saudi authorities.

Many Al Qaeda fighters have been captured by U.S. forces and their Afghan allies. A Saudi official said last week that a small number of Saudis were among detainees transferred to a U.S. military base in Cuba.

The talks also involved the level of Saudi financial aid in Afghanistan's reconstruction. Karzai is scheduled to travel to Japan for a conference of potential international donors this week.

The Associated Press contributed to this report.