The final plug on BP's blown-out oil well in the Gulf of Mexico won't be finished until officials are convinced it's safe to go ahead.

Retired Coast Guard Adm. Thad Allen told reporters Monday that once the order to start the permanent fix is given, it will take about a week before the well is killed for good.

But Allen says he doesn't know when that will be. Scientists are working on strategies to continue without risking further damage to the well.

Allen says there are two likely options right now. One would replace the existing equipment choking off the flow of oil, and the other would build a pressure relief system into the existing equipment.

A cap has kept oil from flowing into the sea for weeks, but the government says a permanent plug is still needed.