WASHINGTON, April 2 (Xinhuanet) -- The US government has warned that there could a potential plot to attack mass transportation systems in major US cities this summer.

    Brian Roehrkasse, spokesman for the Department of Homeland Security (DHS), said Friday that the DHS and the Federal Bureau ofInvestigation had issued a bulletin late Thursday to law enforcement agencies and the private sector after receiving "uncorroborated, nonspecific threat reporting" about such attacks. Enditem