WASHINGTON/VENICE, La (Reuters) – US President  Barack Obama yesterday blamed the massive Gulf of Mexico oil  spill on “a breakdown of responsibility” at energy giant BP Plc  as he officially unveiled a commission to investigate the  disaster.

Obama, in his weekly radio and Internet address, also said  offshore oil drilling could only go forward if there were  assurances that such accidents would not happen again.

While ramping up pressure on firms linked to the still  uncapped spill — BP, Halliburton and Transocean Ltd. — he  said he would also hold Washington accountable for mending its  ways.

With political stakes growing, Obama had his toughest words  yet for companies linked to the spill.

“First and foremost, what led to this disaster was a  breakdown of responsibility on the part of BP and perhaps  others, including Transocean and Halliburton,” he said.

“And we will continue to hold the relevant companies  accountable not only for being forthcoming and transparent  about the facts surrounding the leak, but for shutting it down,  repairing the damage it does, and repaying Americans who’ve  suffered a financial loss,” he said.

A month after the well blowout and rig explosion that  killed 11 workers, sheets of rust-coloured heavy oil are  starting to clog fragile marshlands on the fringes of the  Mississippi Delta, damaging fishing grounds and wildlife.