Image caption Hopes are rising for the first time since the blast

Tests on BP's newly capped Gulf of Mexico oil well show pressure has been building up slightly as hoped with no signs of leakage, BP says.

BP vice-president Kent Wells said rising pressure "is giving us more and more confidence". However, tests have been extended for another 24 hours.

The new cap has managed to stop the flow of oil for the first time since a 20 April explosion killed 11 people.

The spill has been described as the worst environmental disaster in the US.

It has affected hundreds of miles of Gulf coastline since April, with serious economic damage to the region as tourists have avoided Gulf Coast beaches and fishing grounds have remained closed.

BP has put the costs of dealing with the disaster at over $3.5bn.

It has already paid out more than $200m (£130m) to 32,000 claimants. The company is evaluating a further 17,000 for payment and is seeking more information on 61,000 other claims.

Analysis If the pressure readings drop or a leak is discovered from the ocean bed, the valves will once again be opened. This time, though, BP says it is ready with four container ships on the surface to siphon off most if not all the oil. Work on two relief wells which will finally cap the well has restarted. They should be finished in the next few weeks when concrete and mud will be pumped into the well, sealing it for good. Even if all that goes to plan, the Gulf of Mexico still faces a huge clean-up operation that could take years.

The flow of oil was shut off at 1425 local time (1925 GMT) on Thursday, as part of a test of the well's integrity.

If the pressure within the new cap on the well stays high, it could mean there are no other leaks or ruptures within the well bore. If it drops, that could suggest problems.

On Saturday, as the initial testing was coming to an end, Mr Wells told a news briefing: "We're feeling more confident that we have integrity.

"At this point there's no evidence that we don't have integrity.

"That's very good and the fact that the pressure continues to rise is giving us more and more confidence as we are getting through the test."

BP is drilling a relief well which should intercept the leaking one at the end of July, enabling it to be sealed by mid-August.