Serbians are marking the tenth anniversary of the start of the NATO air assault on the capital Belgrade and other major population centers.A decade ago today - NATO launched military strikes on Serbian civilian areas as part of efforts to push the country's forces out of Kosovo - then a Serbian province. NATO said Serb troops had committed atrocities against ethnic Albanians there. Last year, Kosovo unilaterally declared its independence from Belgrade, and relations between the two sides remain tense.