BP says it has begun pumping mud into a breached² Gulf³ of Mexico oil well to try to stem the flow of oil caused by a rig explosion last month.

英国石油公司称，他们正在用泥浆堵住墨西哥湾海底石油油井，该油井上个月因钻探平台爆炸而导致原油泄露。

Oil from the spill is threatening Louisiana's delicate wetlands

The US government had earlier approved the move, a so-called "top kill（顶部压井） ", which has never been tried at such a depth.

BP is under intense pressure to succeed with its latest attempt to stem（阻止，逆行） the leak, after previous measures failed.

Thousands of barrels of oil have been spewing（喷涌，呕吐） into the Gulf every day since the accident on 20 April.

Company officials say it could be a couple of days before they know whether the "top kill" operation is working.

Mud will continue to be pumped into the well for hours, spokesman Steve Rinehart said.

"The procedure is intended to stem the flow of oil and gas and ultimately kill the well by injecting heavy drilling fluids through the blowout preventer（防喷器） on the seabed, down into the well," a BP statement said.

If the oil flow is successfully capped, engineers will follow up with cement（水泥） to seal the well permanently⁴.

BP Chief Executive Tony Hayward has put the operation's chance of success at 60-70%.

The procedure began at 1300 local time (1800 GMT), shortly after federal officials approved the plan.

Officials say the method has been used before in other areas of the world, but not at the depths required to stem the oil from the Deepwater Horizon rig.

There is a risk a weak spot in the blowout preventer that sits on top of the well could breach¹ under the pressure, causing a brand new leak at the site 50 miles (80km) off the Louisiana coast.

'No guarantees'

Speaking in California, US President Barack Obama said his administration would commit all resources necessary to stop the flow of oil into the sea.

"If it's successful - and there are no guarantees - it should greatly reduce or eliminate the flow of oil now streaming into the Gulf from the seafloor. And if it's not, there other approaches that may be viable⁵（可行的） ," he said.

Mr Obama said the "heartbreaking" oil spill underscored the need to find alternative energy sources.

"We will not rest until this well is shut, the environment is repaired and the clean-up is complete," he added.

Mr Obama is due to make his second visit to the Gulf of Mexico region on Friday.

His visit will come a day after he receives a report into offshore⁶ drilling that is expected to recommend tougher regulations and demand more safeguards.