LONDON, Aug 15 (Reuters) - British Prime Minister David Cameron said on Friday he was gravely concerned by reports that Russian military vehicles had crossed into Ukraine and warned the Kremlin not to use an aid convoy as a pretext for stoking the conflict.
Cameron expressed his concerns during a call with Ukrainian President Petro Poroshenko, a spokesman for Cameron's Downing Street office said.
Russia "must not use the aid convoy as a pretext for further provocation," the spokesman quoted the two as agreeing, adding that Russia needed to demonstrate a willingness to end the conflict in Ukraine.
"The Prime Minister expressed grave concerns at reports of Russian military vehicles crossing the border," the spokesman added in a statement. (Reporting by Guy Faulconbridge; editing by Stephen Addison)