By NBF News

The BP well which spilled 206m gallons of oil into the Gulf of Mexico poses no further risk to the environment, says the US official leading the clean-up.

Adm Thad Allen made the announcement after engineers replaced a damaged valve on the sea bed.

The failure of a similar blowout preventer is thought to have caused the oil spill, the worst in modern times.

That faulty device has been brought to the surface and will be examined as part of an enquiry into the leak.

Engineers plan to pump concrete from a second relief well to seal the ruptured well for good.

That operation is expected to begin some time in the coming week.

The flow of oil was stopped more than a month ago, but there had been fears the well could start leaking again under pressure.

BP has pledged $20bn to compensate Gulf residents harmed by the spill, and has pledged millions more to study the spill's environmental impact and to promote tourism in the Gulf Coast states affected.