Kosovo's United Nations governor Soren Jessen-Petersen left empty-handed on Monday after talks with Serb leaders on the fate of more than 3,000 people still missing since the 1998-99 Kosovo war.
Serbia has already found 836 corpses of ethnic Albanians in mass graves far from Kosovo, and on Sunday a senior police official said it was checking reports that Serb police also incinerated Kosovo Albanian corpses in 1999 in a factory furnace.
But the U.N. governor said his meetings had been dominated "exclusively" by Belgrade's complaints about power cuts in two Kosovo Serb enclaves, an issue he said had been politicised.
Jessen-Petersen said the fate of Kosovo's missing was a "burning humanitarian issue" and he deplored the fact that his talks had been sidetracked by an electricity complaint.
"I don't feel we have made today the kind of progress on some very important issues that should have been made," he told a news conference.
He urged a resumption of dialogue on the issue, which Belgrade suspended in the wake of devastating Albanian riots against Serbs and other minorities in Kosovo in March 2004.
"I urged (Prime Minister Vojislav) Kostunica to agree to an early date. I did not get an early date, but I will now come up with one," he said.
Interior Ministry inspector-general Vladimir Bozovic told Radio B92 on Sunday that investigators were probing charges that Albanian bodies had been burned in southern Serbia in 1999.
He hoped "a professional and objective investigation will be completed which will yield results" in the next two months.
Bozovic could not be contacted on Monday for comment.
Allegations that bodies had been burned as well as buried in mass graves came recently from respected human rights lawyer Natasa Kandic.
Citing "independent sources", Kandic says cadavers were incinerated on the nights of May 16 and 24, during NATO's 11-week bombing campaign to drive Serb forces from Kosovo.
She alleges that several police officials still holding senior positions were involved in the operation in the town of Surdulica, 40 kilometres (25 miles) east of Kosovo.
The province, with an ethnic Albanian majority, became a U.N. protectorate in 1999 after NATO expelled Serb forces.
The regime of former leader Slobodan Milosevic is known to have trucked hundreds of bodies from Kosovo to Serbia proper and buried them in mass graves, later discovered and opened.
The existence of the graves was revealed in 2001 as reformers braced Serbs for Milosevic's extradition to the U.N. war crimes tribunal in The Hague.
Serbian authorities have yet to charge anyone for what U.N. prosecutors say was a systematic cover-up. About 2,400 of the 3,000 missing are Albanians. Fewer than half of the remains of those found dead have been returned to their families, a rate the U.N. says is unacceptably slow.