BBC News reports the US secretary of state has rejected an offer of talks with President Vladimir Putin until Russia engages with US proposals on Ukraine's crisis. John Kerry told his Russian counterpart Sergei Lavrov that Moscow's military intervention in Crimea had made any negotiations extremely difficult. US officials say there will be little to discuss if the referendum on whether Crimea should join Russia goes ahead. Ukraine and the West say the vote, due to be held on Sunday, is illegal. Meanwhile, NATO on Monday announced that it is to deploy Awacs reconnaissance planes in Poland and Romania to monitor the Ukrainian crisis. NATO said the surveillance flights would "enhance the alliance's situational awareness." Additionally, both EU leaders and the US have warned Moscow they would impose sanctions if Russian troops remained in Crimea. Officials from several countries are meeting in London to discuss sanctions against Russian officials.