Updated

President Hamid Karzai has sidelined his Afghan bodyguards and called in U.S. troops to replace them in a sign of rising security fears following the murder of an Afghan vice president, his aide said Monday.

Diplomats said the move followed "serious threats" against Karzai, some believed to have come from within his own Cabinet. The approximately 50 guards who were replaced were part of the 10,000-strong force of fighters loyal to Defense Minister Mohammed Fahim.

U.S. Defense Secretary Donald H. Rumsfeld confirmed the move, calling it a "short-term" measure to ensure stability in this country fragmented by 23 years of war.

"We look at it as a relatively short-term matter" to last several weeks or months, Rumsfeld told reporters at the Pentagon. He said the United States also would help train Afghan bodyguards for Karzai.

"Clearly, it is important for that country that the outcome of the loya jirga not be negated by violence," Rumsfeld said, referring to the Afghan grand council which chose Karzai last month to head the two-year transitional government.

Concern over Karzai's safety has soared after the unsolved killing this month of Vice President Abdul Qadir, said presidential spokesman Said Fazel Akbar.

"The investigation into the slaying of Qadir has so far not produced results, and something had to be done to increase the president's security," Akbar told The Associated Press.

Sources at the sprawling downtown palace said the first of about 50 U.S. soldiers, including special forces, started deploying over the weekend to take care of Karzai's personal safety. A U.S. Army spokesman in Kabul, the Afghan capital, declined to comment, and Karzai has made no public appearances since the changeover.

"The people who guarded Karzai in the palace were simple soldiers who don't know much about organizing security," Akbar said. "They will get the proper training (from the Americans), and in a few months, they will take over."

Qadir was gunned down July 6 outside his office by two men who fled in a white vehicle. Ten security guards on duty were arrested for failing to stop the killing or apprehend the two gunmen. No charges have been filed.

Qadir was the second government minister killed in Kabul in six months. Abdul Rahman, the minister of aviation and tourism, was killed in February at the Kabul airport. Witnesses said he was killed by would-be pilgrims furious over delayed flights to Saudi Arabia, but Karzai blamed a plot among high-ranking officials in his own government.

A Western diplomat said on condition of anonymity that Karzai faced "serious threats" not only from remnants of the Taliban and Al Qaeda but from warlords furious over Karzai's recent order to disband their private forces -- whose presence is one of the most serious problems facing the government.

Afghanistan is in the process of training a new multiethnic national army, but those forces will be smaller than many of the private armies maintained by warlords.

Warlords run their enclaves like private mini-states often without regard for the central government, even though some, such as Fahim, have positions in Karzai's administration.

On Monday, Karzai, an ethnic Pashtun, named Fahim as the head of a 12-member commission in charge of forming the new National Army, state TV reported.

The United States is eager to establish a multiethnic national army that will extend government control nationwide. That will allow the Americans to consider withdrawing their 7,000 troops without fear the country will descend into chaos.

However, warlords are reluctant to hand over weapons and troops to the national army. A new, internationally trained battalion provided security for the loya jirga in June, but more than one-third of the soldiers have since left the unit because of lack of support from Fahim's Ministry of Defense, according to the United Nations.

Fahim, an ethnic Tajik who commanded the northern alliance forces that chased the Taliban from Kabul with U.S. help last year, has an estimated 300 tanks and 500 armored personnel carriers at his disposal.

Some Western diplomats consider Fahim's force a possible threat to Karzai's administration, although none alleged he was part of any specific plot. They say that if Fahim wanted to topple Karzai, an ethnic Pashtun, he could easily sweep aside the lightly armed International Security Assistance Force that has been entrusted with Kabul's security.

On Monday, Karzai named Fahim as the head of a 12-member commission in charge of forming the new National Army, state TV reported.

Last Saturday, the international peacekeepers started separate training of 240 Afghan bodyguards to protect Karzai's Cabinet ministers and other senior officials. On Monday, 60 displayed bodyguard techniques on how to protect dignitaries.

"Some of them might protect Karzai as well, if the Afghan authorities decide so," said Turkish Maj. Murat Pekgulec, a spokesman for the international force.