Leaders of Serbia and its breakaway province of Kosovo remain deadlocked over independence, suggesting little chance of a breakthrough at meetings this week.
The politicians refused to give ground on Monday over their demands - Kosovo wants independence, but Serbia refuses - with time running out for an agreement before a December 10 deadline.
The Serb president says he will use all legal means to prevent independence, while Kosovan leaders seem intent on ploughing ahead with independence plans.
Agim Ceku, Kosovo's prime minister, said a team of ethnic Albanian negotiators, including the president and opposition figures, would go to London on Tuesday to discuss plans "beyond independence".
He also said that Kosovo would table a "treaty of friendship" with Serbia.
Kosovo's and Serbia's leaders will hold separate meetings over two days with envoys from the United States, the European Union and Russia.
Ceku said: "We're not ready to have more delays and we demand a decision be made.
"We are going there as a state ... we want to talk about technical issues between two independent states and we want to discuss issues beyond independence.
"If the international community hesitates to make the decision, we are ready and determined to make it, despite all the challenges that might face us."
'No independence'
Boris Tadic, the Serbian president, met Vaclav Klaus, the Czech president, in Prague, on Monday and repeated his country's stand
"Serbia cannot have conditions imposed on itself that affect its sovereignty and integrity," he said.
"We will use all legal and diplomatic means to prevent this [independence] from happening."
After this week's meetings, the diplomats will report to Ban Ki-moon, the UN secretary general. The two sides are also expected to hold face-to-face talks in New York at the end of the month.
The US has said it would recognise a Kosovo Albanian independence declaration, but EU countries remain split on what to do.