The US president has said he is "furious" about the oil spill in the Gulf of Mexico, adding that oil giant BP had not responded quickly enough to disaster.
In an interview with the CNN on Thursday, Barack Obama said BP had felt his anger over the spill but he added "ultimately this isn't about me and how angry I am."
"I would love to just spend a lot of my time venting and yelling at people. But that's not the job I was hired to do. My job is to solve this problem."
Obama said the spill, the largest in US history, was an example of a situation "where somebody didn't think through the consequences of their actions."
"This is imperiling an entire way of life and an entire region for potentially years," he said, adding that he had not seen the kind of "rapid response" from BP that he would have liked.
Obama's comments came as BP engineers continued with efforts to fit a cap over the ruptured undersea pipe that has been spewing oil into the Gulf for over six weeks.
On Thursday after two days of trying the engineers succeeded in cutting through the pipe using a robotic submarine.
Tony Hayward, BP's chief executive, said that severing the pipe was an "important milestone" in efforts to plug the leak.
"We have cleared the riser from the top of the wellhead and the team is working to complete the cleanup operation before we put the cap on top of the well," Hayward said.
He said it should be clear by Friday if the cap had been successfully put in place allowing oil to be funnelled to the surface.
Engineers have battled unsuccessfully to cap or contain the gushing leak since an explosion on April 20 tore through the BP-leased Deepwater Horizon rig just off the Louisiana coast.
Eleven oil workers died in the explosion.
In Thursday's interview Obama fended off ongoing criticism that his administration should be playing a more direct role in managing the spill, blaming a "mistake in understanding."
He said that while the US Coast Guard was responsible for coordinating relief efforts with BP, the government was reliant on the London-based energy giant for its expertise and equipment to plug the broken well.
"My job is to make sure that they are being held accountable, that we get to the bottom of how this happened, that they are paying what they're supposed to be paying, that they cap this well," he said.
In the latest move to counter criticism of the US president's response to the ever-growing disaster, the White House said Obama would make his third trip to the Gulf of Mexico coast on Friday.
The announcement came as the White House said it would be sending BP an initial bill of $69m to pay for the damage caused by the leak, and subsequent clean-up efforts.
|A BP video feed shows an attempt to cut and cap a ruptured pipe at the site [Reuters]
The figure represents 75 per cent of government costs to date, White House spokesman Robert Gibbs said.
That is a small fraction of the $1bn BP says it has spent on the spill so far.
On Wednesday, the giant oil slick was spotted a matter of miles from the tourist beaches of the Florida coast, prompting fears that it will wash ashore in a fourth US state.
So far more than 200km of Louisiana coast have been contaminated, triggering long-term fears for the region's already vulnerable coastal wetlands and native wildlife, including lucrative fishing grounds.
Earlier scientists from the University of Miami released a study showing the oil slick's surface area had expanded to cover 24,435km sq of the Gulf - triple the size of satellite imagery from May 1.
Experts say the best chance of stopping the leak once and for all remains the drilling of a relief well, but that is still at least two months from completion.