British oil company BP has decided to extend its test on the ruptured oil well in the Gulf of Mexico where huge oil leak has so far been temporarily shut off by a new well cap, officials said on Saturday.

"As we continue to see success in the temporary halt of oil from the leak, the U.S. government and BP have agreed to allow the well integrity test to continue another 24 hours," Thad Allen, the U.S. Coast Guard commander in charge of the spill response, said in a statement.

The ongoing test, due to end on Saturday, will continue through Sunday afternoon after the extension.

The test, which involves multiple pressure readings in the well, is designed to check the structural integrity of the blown-out well and to see whether it is structurally sound with no leaks in the seabed.

BP expressed rising confidence as the oil flow was stopped on Thursday.

"We're feeling more comfortable that we have integrity" in the well, said Kent Wells, BP's senior vice president.

BP's so-called "well integrity test" began Thursday after two days of delays, first as government scientists scrutinized testing procedures and then as BP replaced a leaking piece of equipment known as a choke line.

The company said oil stopped leaking Thursday afternoon after engineers gradually dialed down the amount of oil flowing through the last of three valves on the cap.

It is the first time that BP completely stopped the oil leak since the BP-leased Deepwater Horizon drilling rig exploded and sank off the Louisiana coast in late April, killing 11 workers and unleashing the worst oil spill in the U.S. waters.

Once the test is complete, BP will immediately resume siphoning crude oil from the well to the two oil-capture vessels on the surface.

Meanwhile, Wells said Friday work had restarted on the drilling of the first of two relief wells, which is seen as the only permanent way to plug and seal the breached underwater well.