The United Nations says Afghan militia commanders, widely described as warlords, are refusing to give up their private armies - threatening the country's prospects for peace.

Afghanistan's donor countries are pushing the transitional government of President Hamid Karzai to meet its promise of disarming scores of semi-independent militias across the war-ravaged country.

At least 40 percent of such forces are due for demobilization by the end of next month.

But U.N. special representative to Afghanistan Jean Arnault says the militia commanders are needlessly stalling the process and continue vying with each other for power. U.N. spokesman Manoel de Almeida e Silva read Mr. Arnault's statement to reporters in Kabul.

"The program has not yet started, and the possibility that it will be completed in time is now seriously in jeopardy. There is no valid reason to delay the implementation of this important government initiative," he said.

Afghan militias were part of the loose alliance, which joined the United States-led multinational coalition in overthrowing Afghanistan's former hard-line Taleban regime in late 2001, for giving safe haven to the al-Qaida terror network.

The private militias had been left in place in order to provide security across the country until a regular army could be formed.

But two-and-half-years later, many militias remain despite the creation of the Afghan National Army.

Manoel de Almeida e Silva says that between the new army and the various international troops deployed across Afghanistan, the militias have no purpose in terms of keeping security in the country.

"Quite the contrary: many of them have been, in the past two years, involved in factional fighting, which is a continuing cause of instability and suffering for the communities affected by it," he stressed.

The spokesman confirmed the names of some of the militia leaders refusing to disarm - including powerful Afghan commander Ismail Khan, governing the Herat province, and northern militia commander Atta Mohammed.

Many Afghans describe these militia leaders as warlords, with some of them accused of committing serious human-rights abuses in the past.

In his statement, Mr. Arnault warned that if the militias are not disarmed soon, Afghanistan could sink back into the civil wars of the 1990s, when rival armies brought widespread destruction as they vied for control of the country.

The existence of the militias, combined with a low-level Taleban insurgency, has raised questions whether the upcoming historic elections planed for September will be free and fair.