PRISTINA, Serbia (Reuters) - Violence simmered on in Kosovo on Monday as Yugoslav and ethnic Albanian leaders jostled for position ahead of peace talks called by the international community for the weekend. International envoys were due in the province to try to convince ethnic Albanian leaders who have yet to commit to the negotiations outside Paris, called amid fears of widespread fighting if a political settlement is not reached soon. In Paris, French Foreign Minister Hubert Vedrine said he was hopeful peace talks would take place but efforts to set the negotiations up "are extraordinarily difficult." Western diplomats said they were surprised the Kosovo Liberation Army (KLA) had not yet responded unreservedly to the talks invitation. A KLA spokesman reiterated on Monday that the guerrillas wanted a Serb withdrawal from Kosovo first. Yugoslav President Slobodan Milosevic has also yet to give his reply to the call to negotiate, which is backed by NATO threats to bomb Serbian military targets if he does not comply. Diplomats say their biggest fear between now and the start of the talks is of an outbreak of violence in the southern Serbian province that may cause one or both sides to boycott the peace conference. International verifiers said a Serbian armoured brigade, backed by heavy artillery, remained much in evidence at the site of some of the worst clashes around Podujevo, 32 km north of the Kosovo capital of Pristina. A grenade thrown through the window of an ethnic Albanian cafe in Pristina and wounded two others on Sunday evening. It was the city‘s fourth grenade attack in 48 hours. British Foreign Secretary Robin Cook met ethnic Albanian leaders from Kosovo in the Macedonian capital of Skopje on Saturday to deliver a Contact Group invitation to peace talks scheduled to begin in Rambouillet, outside Paris, on Saturday. The invitation was backed by the threat of NATO air attacks on parties who refuse to cooperate. Britain, France and Germany have committed to deploy ground troops in Kosovo to enforce any peace deal finally agreed. Ibrahim Rugova, Kosovo‘s most popular ethnic Albanian leader and the man most associated with non-violent resistance to Serbian rule, has agreed to go to France. Adem Damaci, KLA political representative, has pledged to respond in a few days. The KLA‘s Kosova Press agency on Monday quoted KLA spokesman Jakub Krasniqi as saying the guerrilla group backed negotiations but Serbian security forces should first withdraw from Kosovo and release all prisoners.