The U.S government has demanded immediate clarification from BP over its commitment to pay for costs caused by the oil spill in the Gulf of Mexico. The Obama administration said it wanted to be sure BP would honour commitments not to limit payments for damages to a U.S statutory cap of 75 million dollars. Meanwhile, BP says oil dispersants applied at the source of the leak on Friday have begun to take effect. Mississippi has become the third U.S state to have oil wash up on its coast. Crude has already contaminated beaches in Louisiana and Alabama since a drilling rig blew up on 20 April killing 11 workers. Mr Obama has stopped all new drilling for the moment.