WASHINGTON - US President Barack Obama ignored legal advice from top Pentagon and US Justice Department lawyers, siding with other advisers who said he had legal authority to continue air strikes against Libya without congressional approval, the New York Times reported on Friday.

Citing officials familiar with the administration's deliberations, the newspaper reported the Pentagon and Justice Department lawyers argued that the US bombing runs over Libya, under NATO command, were "hostilities."

As such, Obama would have had to end or pull back the military flights after May 20 since he did not get backing from Congress for them under the War Powers Resolution.

The Times reported that Obama instead latched onto legal advice from inside the White House and the State Department that the bombing missions fell short of "hostilities" and that they could continue without the green light from Congress.

House of Representatives Speaker John Boehner, the top Republican in Congress, is pressuring the White House to detail the advice the Justice Department Office of Legal Counsel provided on the legality of continuing US military activity against Libya, which is officially aimed at shielding civilians there from the forces of Libyan leader Muammar Gaddafi.

The Times story noted that it is rare for a president to override the legal opinions provided by that office.

The White House has acknowledged differences of opinion within the administration on the legal question.

It has maintained that US military activity against Libya is limited, without any plans to commit ground troops. Democrats in Congress, including Senate Majority Leader Harry Reid, have backed Obama's refusal to invoke the War Powers Act and have suggested the Libya mission is likely to end soon.

The 1973 War Powers Resolution was passed during the era of the Vietnam War to set out the powers of the president and Congress regarding US military actions. It prohibits US armed forces from being involved in military actions for more than 60 days without congressional authorization.