The US government has said BP will continue drilling a relief well to permanently plug the blown-out well in the Gulf of Mexico.
But the government's incident commander, Adm Thad Allen, said drilling would not proceed until they were sure it was safe to do so.
Scientists had been analysing tests to see if mud and cement pumped in the top of the well had "killed" it.
When they decide to drill again, it will take 96 hours for crews to resume.
"The relief well will be finished," Adm Allen said. "We will kill the well."
BP said last week its "static kill" procedure, in which mud and cement was pumped into the top of the well, had worked.
But Adm Allen said it was not clear whether that plug that had formed was enough to block the damaged well permanently.
Drilling of the relief well was put on hold this week because of poor weather.
Meanwhile, Alabama's attorney general is suing BP, Transocean, and other companies connected with the oil spill for damages the state has sustained from the disaster.
Attorney General Troy King filed the lawsuits in federal court on Thursday against the wishes of Alabama Governor Bob Riley, who wishes to reach a settlement with the companies outside the courtroom.
The lawsuits claim the companies damaged the state's coast and economy through failing to "adhere to recognized industry standards". BP has not commented on the move.
The relief well is intended for a "bottom" kill" procedure, in which cement would be pumped into the bottom of the damaged well in the hopes of permanently stopping the leak.
The bottom kill procedure follow's BP's static kill operation, which forced special drilling fluid known as mud through the top of the well to try to seal the leak.
President Barack Obama is set to travel to Panama City, Florida, for a family trip on Saturday. The Gulf Coast town witnessed tar balls washing up on its shores after the oil spill.
Mr Obama, his wife, and their two daughters will be visiting the area during a time when summer tourism is down compared with previous years along the coast.
Oil leaked into the Gulf from 20 April when the Deepwater Horizon rig explosion killed 11 workers. The flow was stopped on 15 July, when a cap was used to seal the top of the wellhead.
An estimated 4.9m barrels of oil leaked into the waters of the Gulf over the course of 87 days, with only 800,000 barrels being captured.