British Petrolem has begun a crucial new procedure to plug its blown-out oil well in the Gulf of Mexico, a plan known as "top kill". It comes as the US government says it won't rest until the problem is finally solved.

Top Kill is the latest attempt end the oil spill disaster in the Gulf of Mexico. Undersea robots are being used to pump heavy fluids and cement into the well to block the oil flow.

BP says the company pumps in the materials for hours, but it may be a couple of days before they know whether the procedure is working.

The company's chief executive earlier gave the procedure a 60 to 70 percent chance of succeeding. The procedure has never before been tried at a depth of 1,500 meters.

US President Barack Obama warned Wednesday there are "no guarantees" but said his office won't rest until the leak is stopped.

Barack Obama, US President, said, "As work continues in the next couple of months to complete relief wells, my administration will intensively engage with scientists and engineers to explore all alternative options and we are going to bring every resource necessary to put a stop to this thing."

Meanwhile, the US Interior Secretary says it is BP's responsibility to pay for the environmental and economic costs associated with the spill.

Ken Salazar, US Interior Secretary, said, "When you think about a company that in the last year, made over 16 billion dollars I think they will be good for paying the compensation that is required here."

At the same time, a BP probe says a "fundamental mistake" may have been made before the explosion of the oil rig--Deepwater Horizon, which killed 11 workers last month. The rig's chief mechanic says there may have been a dispute between BP and the staff of Transocean, the rig's owner on fixing a leak on the day of the explosion. Since then, some 7 million gallons of oil are thought to have spewed into the sea.