The White House told congress last night that President Barack Obama has the legal authority to press on with US military involvement in Libya and urged representatives not to send "mixed messages" about their commitment to the Nato-led air war.
Delivering a detailed report to congress to justify Mr Obama's policy on Libya, the administration argued he had the constitutional power to continue the US role against Muammar Gadafy's forces even though congress had not authorised it.
Tensions in Washington over the Libya conflict reflected growing unease over US entanglement in a third conflict in the Muslim world in addition to costly wars in Iraq and Afghanistan and pressure for Mr Obama to clarify the US mission in the North African country.
The 32-page response followed a warning on Tuesday from house speaker John Boehner that Mr Obama was on thin legal ice by keeping US forces involved in Libya for nearly three months without congressional approval.
But the White House insisted that Mr Obama had not overstepped his authority because US military participation in Libya had already been scaled back to a support role that did not require congressional consent.
Mr Boehner accused the president of failing to respect the role of congress in military operations and asked him to explain the legal grounds for the Libya mission, saying that by Sunday he would be in violation of a 1973 law called the war powers resolution if nothing changed.
The US constitution says that only congress can declare war, while the president is commander in chief of the armed forces.
Ten members of Congress filed a legal suit against Mr Obama in federal court yesterday over Libya. The group, led by democrat Dennis Kucinich and republican Walter Jones, challenged Mr Obama's decision to commit US forces to Libya without congressional authorization.
"With regard to the war in Libya, we believe that the law was violated," Mr Kucinich said in a statement.
But senior administration officials briefing reporters argued that Mr Obama was not in violation of the war powers resolution because US forces, which initially spearheaded the assault on Col Gadafy's air defences in March, had pulled back to a support role in the Nato-led air campaign in early April.
"We're not engaged in any of the activities that typically over the years in war powers analysis is considered to constitute hostilities," one official said. "We're not engaged in sustained fighting."
The law prohibits US armed forces from being involved in military actions for more than 60 days without congressional authorisation, and includes a further 30-day withdrawal period, which would expire on Sunday.