NEW : NATO chief : It 's `` the gravest crisis to European security '' since the Cold War . " Russian Foreign Minister Sergey Lavrov calls timing of presidential vote unusual . Russian Foreign Minister Sergey Lavrov on Tuesday ruled out holding a second international meeting in a bid to defuse the crisis in Ukraine , also saying it would be `` unusual '' to hold a presidential election in the country when the army was being deployed against the population . Lavrov rules out second international meeting on Ukraine .
NEW : NATO chief : It 's `` the gravest crisis to European security '' since the Cold War . " Russian Foreign Minister Sergey Lavrov calls timing of presidential vote unusual . Lavrov rules out second international meeting on Ukraine .