"We are classifying this as a very serious spill and we are using all our resources to help contain it," Terrell said .
BP has deployed ships and aircraft to contain the oil slick, which could threaten Louisiana's fragile coastline if it is not contained.
Clean-up operations are currently on hold due to stormy seas, Terrell said.
BP PLC, which leased the rig and is taking the lead in the cleanup, and the government have been using the remotely operated vehicles to try to stop the leak by closing valves on the well deep underwater.
If that does not work the company could have to drill an intervention well to control the oil flow, but that could take months.
"Over the next several days, we should determine which method is the best one to follow," Doug Suttles, chief operating officer for BP
exploration and production, said.
So far, the spill is not comparable with the Exxon Valdez disaster, which spilled about 50 million litres of oil into the Prince William Sound in Alaska when it ran aground in 1989.
The Transocean well is spewing about 190,900 litres of oil a day into the ocean, the coast guard estimates.
The coast guard on Friday suspended a search for 11 missing workersfrom the rig, who are presumed dead.
Manouchehr Takin, from the Centre for Global Energy Studies, London, told Al Jazeera that the explosion was a "tragic accident".
"Accidents occur, this is inevitable. The blowout preventer, an equipment which automatically separates the well from the upper part of the rig - should something like this happen - apparently did not operate, according to speculation," he said.
"These things do occur, they are unfortunate, but I would say it is more of an accident."
The explosion came almost three weeks after Barack Obama, the US president, unveiled plans for a limited expansion of US offshore oiland gas drilling.
The blast could prove to be one of the nation's deadliest offshore drilling accidents of the past half-century.
About 115 of the 126 workers on the rig at the time of the explosion were rescued.
Since 2001, there have been 69 offshore deaths, 1,349 injuries and 858 fires and explosions in the Gulf, according to the US Minerals Management Service.
There are 42 rigs employing an estimated 35,000 people either drilling or doing upgrades and maintenance in depths of over 305 metres or greater in the Gulf of Mexico, according to the agency.
In 1964 an explosion on a drilling barge operated by Pan American Petroleum Corp near Eugene Island, about 130km off Louisiana, killed 21 crew members.
The deadliest offshore drilling accident took place in 1988, when the Piper Alpha platform about 193km off Aberdeen in Scotland, was rocked by explosions and a fierce fire. A total of 167 men were killed.