Oil giant BP, watching tensely with the rest of the world, said on Thursday that so far it had no news to report about the risky attempt to seal off its ruptured well at the bottom of the Gulf of Mexico.

“There are no significant events to report at this time,” the company’s website stated more than 12 hours after engineers began the so—called “top kill” technique to try to plug the damaged well head with heavy mud.

The operations had been carried out overnight and were continuing, and “BP will provide updates on progress as appropriate,” it said.

Five weeks after massive crude oil seepage into the sea, the operation marks the first time that BP has tried to seal off the well.

Earlier attempts to contain the situation focussed on siphoning off the oil as it escaped damaged pipes.

BP chief Tony Hayward noted the danger of making the leak even worse. He said it would take at least until late Thursday before the success of the attempt could be evaluated.

The operation began at 1 pm (1800 GMT) on Wednesday, after the US Coast Guard gave the go—ahead.

BP chief operating officer Doug Suttles said late Wednesday that about 7,000 barrels of mud were pumped into the well in the first six hours of the top kill effort: “The job has been proceeding according to plan.” Underwater cameras documenting the leaks have been obscured at times by escaping mud, which Mr. Suttles said was expected.

Weeks of talk about top kill have built up expectations. BP officials warned against hopes for a quick fix, while rating their own chances at up to 70 per cent for success.

Independent of the result of the top—kill operation, US President Barack Obama was scheduled on Thursday to announce sharply tightened regulations for offshore oil drilling. The focus is on stricter safety standards and controls on oil rigs.

On Wednesday Mr. Obama had noted a wide “sense of despair” about the unfolding environmental disaster. Mr. Obama is to tour the oil— slicked coast on Friday for a second time to assess efforts.