They also have rejected a Western-backed plan granting internationally supervised independence to Kosovo.
Wolfgang Ischinger, the German negotiator, told The Independent newspaper: "I would leave open independence. I would rather talk about a strong supervised status."
Sejdiu said: "The issue of Kosovo is on the agenda, Kosovo's independence is on the agenda [and] our determination to achieving it has no alternative."
Vuk Jeremic, the Serbian foreign minister, called on all parties to exercise caution.
"Unilateral moves regarding Kosovo would be very dangerous and have dramatic consequences to peace and stability in the Balkans."
Sergei Lavrov, Russia's foreign minister, warned against rushed decisions on Kosovo's independence, rejected a December 10 deadline for the Serbs and the Albanians to reach a compromise.
"We don't consider it possible to have any kind of artificial deadlines," Lavrov said after talks with Bernard Kouchner, the French foreign minister, in Moscow.
"After all, we haven't had any deadline for the creation of a Palestinian state even though the Palestinians have been waiting for it for 60 years."
Speaking after his talks with Lavrov, Kouchner voiced hope that the Serbs and Kosovo's ethnic Albanians could reach a consensus.
He said later on Ekho Moskvy radio that the talks could be extended by another six months if no deal is reached.
The Contact Group is to report to Ban Ki-moon, the UN secretary general, on the progress of the talks by December 10.