US President Barack Obama said possible safety shortcomings might have led to the rig explosion causing oil to leak in the Gulf of Mexico at the rate of 19,000 barrels a day.
US attorney general Eric Holder has opened a criminal investigation into the accident and promised prosecutions to the fullest extent of the law, according to Bloomberg.
The oil spill has damaged about 140 miles of shoreline in Louisiana, Alabama and Mississippi and some 80 miles in Florida.
BP has so far spent $1.25bn on the oil-spill response.
BP said it captured 11,100 barrels on 6 June from the ruptured well on the ocean floor, almost half of the top end of the estimated spill rate.