Kosovo's president said he's counting on NATO's promise to secure the new nation's borders and help provide stability as Serbia angrily challenges its independence. Fatmir Sejdiu told The Associated Press in his first post-independence interview Thursday that NATO's assurances that it won't abandon Kosovo provide a "powerful guarantee" for stability. The Western military alliance has about 16,000 peacekeepers in Kosovo. Sejdiu warned Serbia that any attempts to partition the fledgling country along ethnic lines will bring what he called "grave consequences" to the region. He spoke as hundreds of Serbs staged boisterous protests for a fourth day since Kosovo's ethnic Albanian leadership declared independence Sunday. "There is a part of society that wants to destabilize Kosovo and create alarming, hopeless situations and scare the international community," Sejdiu told the AP in his office decorated with Kosovo's new flag. "Any change of borders brings extremely grave consequences for the region, and someone then has to be held accountable." Echoing Sejdiu's concerns, German Foreign Minister Frank-Walter Steinmeier stressed Thursday that preventing the division of Kosovo is essential.