President Barack Obama is concerned about Greece’s debt problems and his administration is in touch with Europe about the issue, White House spokesman Bill Burton said on Wednesday. “This is something that is of great concern to the president and we’re monitoring it very closely,” Burton told reporters on Air Force One, adding that the U.S. Treasury Department and other agencies were “in close contact with folks in Europe about the issue.” German Chancellor Angela Merkel said earlier on Wednesday negotiations with Greece over a planned aid package for the country should be accelerated because the stability of the euro zone was at stake.