President Vladimir Putin said Monday that Russia is sending an aid convoy to eastern Ukraine despite urgent Western warnings against using humanitarian help as a pretext for an invasion.

With Ukraine reporting Russia has massed 45,000 troops on its border, NATO said there was a "high probability" that Moscow could intervene militarily in the country's east, where Kiev forces are closing in on pro-Russian separatists.

European Commission President Jose Manuel Barroso delivered a blunt message in a telephone call with Putin on Monday. "President Barroso warned against any unilateral military actions in Ukraine, under any pretext, including humanitarian," the commission said in a statement.