BP said Saturday that it began removing drill pipes and other equipment from the damaged wellhead in the Gulf of Mexico, as it prepares to replace its giant blowout preventer valve with a new one.

Called a "fishing" procedure, the pipe removal was authorized late Friday by US spill response chief Thad Allen after a successful 48-hour "ambient pressure test" to ensure that no oil would leak during the procedure, BP said.

Allen also gave BP until Sunday to submit a proposal for removing the blowout preventer that won't interfere with a federal investigation into the April 20 explosion that unleashed the worst oil spill in US history.

A so-called bottom kill operation to permanently seal the ruptured well has been delayed until the blowout preventer is replaced.

Originally scheduled for mid-August, the bottom kill was postponed until at least the second week of Sep-tember because of concerns about pressure at the drill site.

The ruptured Macondo well was capped July 15, and earlier this month BP engineers performed a "static kill" that plugged it with heavy drilling fluid and then sealed it with cement.

However, there is an area between the well and the outer well bore called the annulus that must still be sealed off from the reservoir miles below the surface of the Gulf of Mexico.

Engineers are worried that upon removing the blowout preventer, the pressure behind the annulus could increase too quickly and compromise the cement plug above it.

In reference to the delicate blowout preventer removal, Allen told BP "the procedure may not be com-menced without my prior approval."

He ordered BP to provide "continuous live," remote video coverage of the operation, as well as "unfettered access" to federal investigators to observe and record the entire process.