Foreign Secretary Philip Hammond said he is "alarmed" by reports that Russian military vehicles crossed into Ukraine overnight, suggesting it could have "very serious consequences".
Reports suggest more than 70 pieces of military hardware have crossed the border, as Ukrainian officials began to inspect trucks containing humanitarian aid heading to eastern Ukraine.
"I'm very alarmed by reports that Russian military vehicles may have crossed the border this morning," he told reporters at a European Union foreign ministers' meeting.
"If there are any Russian military personnel or vehicles in eastern Ukraine, they need to be withdrawn immediately or the consequences could be very serious."
More top news
Unite leader Len McCluskey is stepping down and will seek re-election for a further term of office from next April, the union said.
Garments belonging to a 'large man' and other personal belongings were found abandoned on Eastney seafront in Hampshire.
The footballer said he was "one of the lucky ones" and was never aware of historical child sex abuse.