US officials finally declared BP’s broken oil well in the Gulf of Mexico “dead”yesterday, five months after the deadly explosion that set off one of the costliest and largest environmental disasters ever.

Retired admiral Thad Allen, the US pointman for the response to the disaster, said the operation to intersect and cement the deepwater well had been successfully completed.

“With this development, which has been confirmed by the Department of the Interior’s Bureau of Ocean Energy Management, we can finally announce that the Macondo 252 well is effectively dead,” Allen said.

“Additional regulatory steps will be undertaken but we can now state, definitively, that the Macondo well poses no continuing threat to the Gulf of Mexico,” he added.

The announcement marked an anti-climactic end to a five-month battle to cap a busted undersea well that gushed 4.9 million barrels of oil into the Gulf of Mexico, the largest maritime spill ever. No oil has leaked into the Gulf in the three months since the well off the Louisiana coast was plugged in a so-called “top kill” operation, but the US administration insisted that it also be sealed from the bottom with a relief well.

A final pressure test of the cement seal was completed at 5.54 a.m. (1054 GMT), officials said.

“Today, we achieved an important milestone in our response to the BP oil spill – the final termination of the damaged well that sat deep under the Gulf of Mexico,” President Barack Obama said in a statement.