BRUSSELS (Reuters) - NATO forces should seal the border between Albania and Kosovo and build up troop strength in neighbouring Macedonia, the former international peace envoy to Bosnia, Carl Bildt, said on Tuesday. Writing in the London-based Financial Times, Bildt charged that NATO was prevaricating while Kosovo slid towards open war. "The reluctance of NATO to deploy forces in northern Albania has impaired efforts to work towards a settlement," he said. "NATO has made clear that it is ready to use its air power against Serbia. But it has little leverage over Kosovo‘s ethnic Albanian separatists. This seriously undermines the possibility of political progress." Guerrillas of the Kosovo Liberation Army (KLA) have used northern Albania with impunity as their rear base for armed infiltration of the Serbian province where they are fighting for independence for the 1.6 million ethnic Albanian majority. Albania‘s ill-equipped army and police have been unable to exert state control in the remote region or prevent guerrilla activities including incursions. NATO earlier looked at the possibility of securing the Albania-Kosovo border but military chiefs discarded it, said it would take several tens of thousands of troops to do the job effectively. The alliance was also concerned about the impact of such a move on the even-handedness of international efforts to secure peace in Kosovo, as well as potential destabilisation of the government of Albania, where the cause of independence for Kosovo is popular and the government weak. But with neither side in the conflict showing any real interest in peace talks, and without outside pressure, Bildt said "there is virtually no prospect of the opponents coming to an agreement by themselves. They are both bent on conflict." The presence of unarmed international observers in Kosovo, a NATO air verification mission and an alliance "extraction force" in Macedonia were clearly not enough, the former Swedish premier added. The threat of NATO air strikes in October persuaded Yugoslav President Slobodan Milosevic to wind up a military offensive against the KLA and reduce troop strength in Kosovo. But the KLA exploited the situation to grab territory. In what international observers characterised as deliberate provocations, the KLA killed three Serbian police in an ambush last week and are now holding eight Yugoslav army soldiers prisoner in a bid to exchange them for captured guerrillas. Bildt said NATO could hardly demand a military pull back by Belgrade if KLA fighters were crossing the Albanian border. Unless NATO raised the military stakes to give itself more leverage, the alliance could find itself celebrating its 50th anniversary in April "facing their first failure to deter war in a generation".