BP's $69M oil spill bill just first invoice: Obama

President Barack Obama has insisted he is "furious" about the US oil disaster as the government sent BP a 69-million-dollar bill, warning it was only the first invoice, while undersea robots tried to curb the leak.

Obama said "yelling" would be pointless as aides rejected claims the president had shown insufficient emotion over the crisis and disputed a media narrative that political trauma over America's worst environmental catastrophe would crimp his agenda.

Fresh, graphic images emerged Thursday of helpless coastal birds writhing in thick oil along Louisiana's coast -- likely to sharpen media anguish.

"I would love to just spend a lot of my time venting and yelling at people, but that is not what I was hired to do -- my job is to solve this problem," Obama told CNN, adding he was "furious at this entire situation."

In the latest move to demonstrate engagement with the ever-growing disaster, the White House said Obama would make his third trip to the Gulf of Mexico coast on Friday.

His spokesman Robert Gibbs said earlier Thursday the federal government was invoicing BP "for 69 million dollars of expenses incurred up to this point."

Gibbs said the bill was to reimburse American taxpayers for the government's costs so far in battling the worst oil spill in US history, with thousands of barrels of oil pouring into the Gulf every day.

In a ray of good news, BP engineers managed to slice off the rig's fractured riser pipe with a pair of giant shears and were preparing Thursday to cover the jagged hole with a cap topped with a siphon and linked to a surface ship.

"We have cleared the riser from the top of the wellhead, and the team is currently working to complete the cleanup operation before we put the cap onto top of the well," under-fire BP chief executive Tony Hayward said.

"It's an important milestone," he added.

But he warned it could take 12 to 24 hours after the cap is put in place to know if it is managing to contain the worst of the spill, amid warnings that with the broken pipe cut off, the oil flow would increase initially.

"In some senses... it's just the beginning. It's been an extraordinary endeavor on the part of many, many people," Hayward said.

BP has battled unsuccessfully to cap or contain the disastrous leak since an April 20 explosion tore through the BP-leased Deepwater Horizon rig just off the Louisiana coast.

Hayward acknowledged earlier in an interview with the Financial Times that the British energy giant had been unprepared for the disaster and "did not have the tools you would want in your tool kit."

The US government has estimated the flow of oil before the riser was cut away at 12,000 to 19,000 barrels a day -- meaning between 22 million and almost 36 million gallons have already poured into the Gulf.

By comparison, Alaska's 1989 Exxon Valdez disaster saw a 11-million-gallons spill.

BP's operation to drill two relief wells -- seen as the only way to permanently cap the failed wellhead -- is on target to be completed in mid-August, US officials said.

The slick, floating along in a myriad of oily ribbons, is now threatening Alabama, Mississippi and Florida after contaminating more than 125 miles (200 kilometers) of Louisiana coastline.

With the slick expected to arrive within days in the Florida panhandle, Coast Guard investigators were also probing unconfirmed reports that tar balls and an oily substance had been found in the tourist-heavy Florida Keys.

Meanwhile, Admiral Thad Allen, who is coordinating the government's response to the spill, said nearly one million gallons of dispersants have been used to break up the oil in the Gulf.

"We're approaching the million gallon mark and it's a milestone and there are concerns about that and we will continue to work the dispersants very, very closely."

Many environmentalists have voiced concern over the unprecedented use of so much dispersant, warning its long-term effect on wildlife -- already threatened by the huge oil spill -- is unknown.

A University of Miami study showed the oil slick's surface area now stretches across 9,435 square miles (24,435 square kilometers) of the Gulf -- about the size of Rwanda and triple the size of satellite imagery from May 1.

Experts also warn the majority of the oil is contained in vast underwater plumes that cannot be measured from above.

US officials have closed more than a third of Gulf of Mexico waters, extending a fishing ban to 88,502 square miles (229,219 square kilometers) -- about 37 percent of the Gulf's federal waters.