Washington, Sep 20 (DPA): The final seal on BP PLC's ruptured oil well in the Gulf of Mexico is finally complete, the US official in charge of the disaster said Sunday.

Five months after the worst marine pollution disaster in US history began, tests showed that the final cement plug of the well 4,000 metres under the floor of the ocean was holding, said Thad Allen, the retired head of the US Coast Guard who is directing the recovery operations.

"I commend the response personnel, both from the government and private sectors, for seeing this vital procedure through to the end," said Allen in a statement. "And although the well is now dead, we remain committed to continue aggressive efforts to clean up any additional oil we may see going forward."

BP chief executive Tony Hayward, who came under firing for the handling of the disaster and will step aside next month, said, "This is a significant milestone in the response to the Deepwater Horizon tragedy and is the final step in a complex and unprecedented subsea operation - finally confirming that this well no longer presents a threat to the Gulf of Mexico."

The British oil giant said it would continue to work to clean up the damage and to share knowledge to prevent a similar disaster in future.

President Barack Obama welcomed the news, but stressed that the government remained committed to cleaning up the region and mitigating any environmental and economic damage.

"Today, we achieved an important milestone in our response to the BP oil spill ­the final termination of the damaged well that sat deep under the Gulf of Mexico," Obama said, congratulating those who worked "around the clock to respond to this crisis and ultimately complete this challenging but critical step to ensure that the well

has stopped leaking forever".

The cement pressure test was completed at 5:54 a.m. local time (1154 GMT) and confirmed by the US Department of the Interior's Bureau of Ocean Energy Management.

The explosion of the Deepwater Horizon oil rig in April killed 11 workers and is believed to have led to the release of 4.9 million barrels of oil into the Gulf of Mexico, the worst environmental disaster in US history.

Images of oil spewing into the water and washing onto beaches captivated the US for months as BP made multiple failed attempts to seal the well.

A temporary cap halted the flow of oil in July, but officials said they could not call the well finally closed until they completed further sealing efforts that ended this weekend.

In August, the so-called static kill forced mud and cement down the ruptured well pipe allowing the removal of the cap. The second step, known as bottom kill, began earlier this week when a relief well intersected with the ruptured well four km below the ocean floor. Engineers finished Friday night pumping cement in at the bottom of the well.

"Additional regulatory steps will be undertaken but we can now state, definitively, that the Macondo well poses no continuing threat to the Gulf of Mexico," said Allen.

BP will now begin removing equipment from the site.

Some $9.5 billion have been spent so far in response to the spill, BP said.