U.S. Homeland Security Secretary Janet Napolitano said Thursday an oil spill in Gulf of Mexico is a disaster of "national significance," and the government is working to minimize its effect.

Napolitano also said that British oil giant BP, which leases the Deepwater Horizon platform that sank into the ocean last week, should be responsible for the damage.

"As the president and the law made clear, BP is the responsible party. It is required to fund the cost of the response and clean- up operations," she said with other top officials at a special White house briefing on the oil spill that might cause environmental disaster if not well addressed.

White House spokesman Robert Gibbs meanwhile told reporters that President Barack Obama received a 20-minute update on the spill at his daily briefing in the Oval Office.

"We will use all available resources, possibly including those at the Department of Defense," said Gibbs.

Louisiana Governor Bobby Jindal on Thursday declared a state of emergency due to the oil spill that could be disastrous for the state's coastal environment and fisheries industry.

The declaration enables the state to ask for more federal aid and mobilize state resources to better prepare for the potential catastrophe.

An explosion occurred last Tuesday at the Deepwater Horizon rig off the Louisiana coast. 11 workers were presumed dead. The Coast Guard initially said no oil appeared to be fleeing from the well on the ocean floor, but officials found oil was leaking Saturday.

According to the Coast Guard, approximately 5,000 barrels of oil is spilling from the rig into the Gulf of Mexico a day -- five times BP's earlier estimate.