According to Pentagon officials in Washington, The Yugoslav President Slobodan Milosevic has now deployed up to 18,000 troops into Kosovo, almost double the number agreed at last October's moribund ceasefire deal, while between 16,000 and 21,000 are waiting just across the border. In addition, at least eight of Belgrade's top-of-the-line M-84 battle tanks, updated versions of the Soviet-era T-72s, have been moved into the province for the first time.
General Wesley Clark, Nato's supreme commander in Europe, claimed before the House Armed Services Committee that the build-up proved that Serb forces were preparing to "resume the conflict on a very large scale" should the second round of talks fail and Belgrade conclude that the alliance did not have the nerve to go through with its threats of airstrikes.
And last night in Paris, failure seemed the most likely - indeed the almost inevitable - outcome. "Time and our patience are running out," James Rubin, US State Department spokesman said, warning that Serbia faced the choice "between peace and catastrophe". The response from the Serbs was as unbending as ever.
Far from inducing concessions, the promised signature by the Kosovo Albanians of the proposed accord has merely stiffened Belgrade's intransigence. Milan Milutinovic, the Serbian President who is heading the delegation in Paris, is still flatly refusing to sign the military annex allowing the stationing of 28,000 Nato-led peacekeepers. He has also demanded sweeping changes in the draft agreement, granting Kosovo wide autonomy.
Having seemed ready at the end of the inconclusive February conference at Rambouillet, the Serbs now object to a key provision of the draft, giving the Albanians the right to have their own police force. They are also seeking to reduce the powers of a future elected Kosovo assembly. "They want to amend 70 per cent of the package," an Albanian negotiator declared.
But with the international mediators representing the six-nation Contact Group of leading powers refusing all but the most minor changes, deadlock is all but complete. Christopher Hill, the chief negotiator and architect of the draft accord, declared bleakly last night that he expected "no further progress".
If so, then the formal signing of the deal by the Albanians could take place as early as today, and barring a last minute cave-in by Belgrade, the talks could finish by the weekend. At that point Nato would again face the stark choice: to bomb or not to bomb. The US is adamant on the former; Mr Milosevic, supreme practitioner of brinkmanship, believes divisions in the alliance will produce the latter result.
Most immediately worrying, however, is the troop build-up. on the ground. Alliance planners simply do not believe the Yugoslav President would take the risk of attacking the 12,000 Western troops (3,800 of them British) already stationed in neighbouring Macedonia. Their immediate task, if talks fail, would be to carry out the evacuation of the unarmed international peace monitors in Kosovo. That would amount to a declaration of war on Nato.
But with spring only a week or two away, Mr Milosevic now has in place the wherewithal for a massive offensive at short notice against the Kosovo Liberation Army (KLA), that would eclipse the crackdowns of last year. That would provoke the "humanitarian disaster" Nato has vowed to prevent.
An independent forensic report has concluded that at least 40 unarmed civilians were killed in cold blood on or around 15 January in the Kosovo village of Racak. Dr Helena Ranta, the Finnish pathologist who led an EU forensic team, did not accuse the Serb authorities of a "massacre". But she noted that normal police investigation procedures were ignored and concluded that the victims were unarmed civilians. The Serb authorities suggested they were armed combatants, and that some died in cross fire.
Although 45 bodies were discovered in Racak, only 40 were presented to Dr Ranta's team for autopsy.