At the White House on Wednesday, retired U.S. Coast Guard admiral Thad Allen attends a news briefing on the BP oil spill. (Larry Downing/Reuters)

BP engineers have successfully plugged the hole at the bottom of the Gulf of Mexico with mud and cement, sealing it permanently, the company said Thursday.

The company started pumping cement into the well Thursday morning — a process known as a "static kill" — after receiving approval from U.S. officials on Wednesday.

By 2:15 p.m. E.T. on Thursday, the company said it had pumped enough concrete and heavy mud into the hole to push the oil back to its original reservoir. Crews will now wait about a day for the cement to dry.

Executives say the static kill may permanently plug the well. But either way they plan to pump mud and cement through a relief well this month to forever suffocate the source of the oil.

"This is not the end, but this will virtually assure us that there will be no oil leaking into the environment," retired U.S. Coast Guard admiral Thad Allen, the government's point man on the oil spill disaster, said during a news conference Thursday.

On Wednesday, U.S. President Barack Obama said the long fight to "stop the leak and contain the oil is finally close to coming to an end."

The president reiterated the importance of the recovery effort and said the government will continue to hold polluters accountable for the damage caused by the Gulf oil spill.

The spill began more than three months ago after an offshore drilling rig exploded, killing 11 workers and creating an ecological catastrophe.

BP temporarily stopped the flow of oil into the Gulf on July 15, when it placed a custom-built cap over the blown-out well. That was always designed to be a temporary solution until the permanent seal could be made.

With files from The Associated Press