Washington, July 18 (DPA) BP Plc and the US government agreed Saturday to extend pressure testing on the new cap sealing the leaking oil well in the Gulf of Mexico, which was holding with no reports of fresh oil flowing.

BP's 48-hour window for pressure testing the cap expired Saturday afternoon, and further testing will now go on through Sunday afternoon.

"As we continue to see success in the temporary halt of oil from the leak, the US government and BP have agreed to allow the well integrity test to continue another 24 hours," said Coast Guard Admiral Thad Allen, who is managing the government's response to the disaster.

He said the federal science team overseeing BP's well integrity test had gleaned valuable information that "will inform the procedure to kill the well and a better understanding of options for temporary shut in during a hurricane".

The government also ordered additional monitoring of the area while the test continues, including doubling seismic mapping over the well site. A sonar ship at the site was to help in monitoring the entire sea floor area around the well.

The cap - the first successful attempt to stop the catastrophic leak - was put in place late Thursday on the ruptured well.

While pressure readings were slightly below levels that authorities had hoped for, they remained "consistent" with a well that had not sprung any extra leaks.

The goal is to make sure that the 4-kilometre-long pipe reaching from the sea floor to the well bottom is not springing any leaks.

President Barack Obama Friday said the temporary stoppage was "good news", but cautioned that the job would not be finished "until we actually know that we've killed the well".

"The new cap is good news as we'll either use it to stop the flow or use it capture all of the oil until the relief well is in place," Obama said.

But the cap is only a temporary solution. BP hopes a relief well that could permanently seal the damaged well will be finished by mid-August.

When the pressure test is eventually stopped, Allen said "we will immediately return to containment, using the new, tighter-sealing cap with both the Helix Producer and the Q4000 (vessels). Additional collection capacity of up to 80,000 barrels per day is also being added in the coming days".

He indicated continued progress on the two relief wells BP was drilling. "The relief well remains the ultimate step in stopping the BP oil leak for good," Allen said.

The disastrous ecological impact on the Gulf waters and coastline has dealt a painful blow to the economy of four states.