PHNOM PENH: Cambodia's Khmer Rouge war crimes court has been dogged by controversy since its creation but now the UN-backed tribunal faces a potential threat to its very existence -- it has run out of money.

The court's 2013 budget still has not been approved by international donors, who have appealed in vain for Cambodia to provide extra funding before they inject more money themselves.

While the contracts of the tribunal's international staff have been extended until June, about 270 Cambodian employees -- including drivers, prosecutors and judges -- have received no pay since November.

The court, whose top donors include Japan, the European Union, Australia, France, Germany and Britain, urgently needs $9.5 million for 2013.

A relatively small amount on paper but a fortune given the strained relations between the donors and the government, accused of doing nothing to save the court, which is trying top leaders of the murderous, hardline communist regime that ruled the country in the late 1970s.

"There is a certain weariness among donors who are fighting to finance the tribunal and often have the impression that the government is not fully mobilised on the issue," said a foreign diplomat who did not want to be named.

"Nobody seems to have money to pay."

Other court observers talk of a standoff between the donors and the government of strongman Hun Sen, a former Khmer Rouge cadre who defected and went on to become prime minister in 1985.

"There are two cars driving full speed at each other to see who will be the one who makes a turn first to avoid the crash," a foreign official at the court said on condition of anonymity.

Set up in 2006 after years of negotiations, the tribunal has so far survived controversy over allegations of corruption, political interference and slow progress in achieving justice, as well as a string of high-profile resignations.

Led by "Brother Number One" Pol Pot, who died in 1998, the Khmer Rouge wiped out nearly a quarter of the population through starvation, overwork or execution in a bid to create an agrarian utopia.

Ex-foreign minister Ieng Sary, "Brother Number Two" Nuon Chea and one-time head of state Khieu Samphan are on trial and deny charges of war crimes, genocide and crimes against humanity.

Health fears have long hung over the court with the octogenarian defendants all suffering from varying ailments.

The tribunal has so far spent $179 million but has achieved just one conviction, sentencing former prison chief Kaing Guek Eav, better known as Duch, to life in jail for overseeing the deaths of some 15,000 people.

Although the cost seems high for a country as poor as Cambodia, it is still far less than that of the International Criminal Tribunal for Rwanda (ICTW), whose budget was $172 million for the financial year 2012-13 alone.

But since its creation by the UN in 1994, the ICTW has delivered 55 verdicts.

While trials for mass crimes are by their nature onerous, the task is crucial to tackle impunity and rebuild society, according to Heather Ryan, a trial monitor at the Open Society Justice Initiative.

"It's almost a game of chicken between the government and the donors," she said. "The donors generally have put so much money in. It would not look good for the donors if after so many years the court would collapse."

Cambodia's neighbours have shown no sign of reaching into their pockets and Hun Sen has not asked them to do so, according to the diplomat. As for his own government, it says that it has already done its duty.

Government spokesman Ek Tha said it "has no budget" available to pay the court staff and has "contributed its maximum effort", doling out $1.8 million for 2013, more than three times the figure for 2006.

From 2006 to 2012 Cambodia contributed a total of $16.9 million, he added.

"We cannot let this crisis go on and on. That is why we are seeking more financial support from new donors and friends of the court," he said. "We are optimistic that the international community will not let this court down."

The tribunal has been frequently cash-strapped since it was set up to find justice for the deaths of up to two million people under the Khmer Rouge.

In late 2011, it ran out of funds to pay hundreds of Cambodians workers until it received new funding from Japan in March last year.

This time, some Cambodian employees have threatened to go on strike -- a scenario that observers say could not come to fruition without the government's implicit agreement.

To avoid a fiasco, observers say, money must be found to avoid the judicial process being derailed.

"It seems that the international community has decided it would not allow the court to collapse," said the foreign court official. "If you start cancelling some court hearings, then of course the money will come."