"We have to be realistic", said Mr Kramer explaining that a solution in December would also imply a change in the Russian position on the issue. "At the moment we haven't seen a shift" from Moscow's side, he pointed out.

Russia is currently Serbia's most loyal ally on the international scene – Belgrade is refusing to consider the breakaway province as anything other than an integral part of its territory and has ruled out any possibility of total independence for Pristina.

For its part, Moscow fears a unilateral declaration of independence by Kosovo would trigger "a chain reaction" in other parts of the world, notably in some of its own breakaway provinces.

Countering this point, Mr Kramer said: "Kosovo is not a precedent. It's not a precedent for any separatist region in Russia or anywhere else (…) Kosovo is a different situation."

He also dismissed comparisons between the province and other parts of the world where similar situations have remained unsolved for years, such as the Middle East and particularly the status of the Palestinian territories.

On top of that, the official warned that the Kosovo issue, among other issues of common concern to both Moscow and the West, is likely to get entangled in electoral campaigns in Russia in the run-up to the parliamentary elections there on 2 December and the presidential ones in March next year.

"There will be a growing focus and even obsession, perhaps, in Russia with the elections issue and succession and that probably will make our relationship a little more complicated", Mr Kramer stated.

However, a stalemate on Kosovo would be dangerous.

The Kosovo deadlock should be broken "sooner rather than later", as "we have concerns that an endless process will lead to a resumption of hostilities that none of us wants to see".

To avoid such a situation, there may be a need to have a solution after 10 December "that not all parties will like".

"That's a possibility - in fact, I think it's likely", the official said.

Meanwhile, international mediators from the "troika" – the EU, the US and Russia - met Serbian and Kosovan representatives on Tuesday and Wednesday respectively in London, but no progress was made.

"At the end of the day we will do it", Kosovan prime minister Agim Ceku said on getting independence. "We will make it happen", he added.

Both sides are to meet for face-to-face talks in a week's time, on 28 September, in New York.