Associated Press WriterBAGRAM, Afghanistan (AP) -- Britain's Royal Marines joined the search for Taliban and al-Qaida fugitives in eastern Afghanistan, officials announced Tuesday, marking the combat debut for an elite force trained to operate in small units in mountains that rise above 10,000 feet.

In Kabul, meanwhile, interim leader Hamid Karzai arrived in Rome to accompany former king Mohammad Zaher Shah -- widely seen as a unifying figure -- back to Afghanistan after 29 years in exile.

The British troops join American and Afghan forces who have already been searching for Taliban and al-Qaida remnants in the mountains near the border with Pakistan in what the U.S. military calls Operation Mountain Lion.

British spokesman Lt. Col. Paul Harradine gave few details, saying only that Britain's Operation Ptarmigan -- named after a Scottish bird that's good at camouflage -- began several days ago in an area "that was formerly known as an al-Qaida and Taliban base."

"They're going to sweep through, destroy any al-Qaida and Taliban that are there and then deny the group control of that area," he said at the allied base here.

U.S. military spokesman Maj. Bryan Hilferty would not say how many American troops were in the area following up on last month's Operation Anaconda -- a 12-day assault on Taliban and al-Qaida forces in the eastern Shah-e-Kot mountains.

Harradine refused to say whether there had been any clashes so far but said the coalition had suffered no casualties.

In Kandahar, a U.S. Army spokesman, Maj. Ignacio Perez, said all U.S. troops had been accounted for following the accidental explosion that killed four U.S. soldiers and wounded one at a demolition range next to the former residence of Taliban supreme leader Mullah Mohammed Omar.

Troops were handling large caliber rockets which had been confiscated from former Taliban ammunition dumps when the accident occurred at midday Monday. The injured soldier was flown to the U.S. military base at Kandahar airport, where officials said his injuries were not life-threatening.

The Pentagon identified the victims as Staff Sgt. Brian T. Craig, 27, of Texas, Staff Sgt. Justin J. Galewski, 28, of Kansas., Sgt. Jamie O. Maugans, 27, of Kansas, and Sgt. 1st Class Daniel A. Romero, 30, of Colorado. Their hometowns were not provided.

Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said the accident shows "our servicemen and women remain at risk" in Afghanistan.

"We certainly want to express our sorrow and grief to the families of those that have been killed and injured," Defense Secretary Donald H. Rumsfeld told a Pentagon briefing Monday. "And we salute the brave men and women in uniform who do, in fact, put their lives on the line every day to defend their country."

Karzai's mission to fetch the deposed king -- a distant relative -- began Tuesday despite concerns over security in the country four months after the collapse of Taliban rule here. Zaher Shah's trip was delayed last month because of a rumored assassination plot.

Karzai's spokesman, Yusuf Nuristani, said the king was expected in Kabul on Thursday. Several ministers accompanied Karzai on the trip.

The 87-year-old former monarch, who has lived in Italy since he was deposed in 1973, is expected to convene a grand council, or loya jirga, in June to choose a new government to rule Afghanistan until elections are held.

After the reported assassination plot last month, security has been beefed up for Zaher Shah. In Kabul, he will be guarded by 40 Afghan bodyguards trained in the past two weeks by Scandinavian troops. The roof of the villa where he will live has been reinforced against attack.

"His majesty doesn't have any concerns. He is going to see his children, his countrymen and women," said spokesman Hamid Sidiq. "He doesn't have any fears in this regard."