A bipartisan group of US lawmakers filed suit against President Barack Obama on Wednesday, saying US military operations in Libya are "illegal" because they do not have congressional approval.

Democrat Dennis Kucinich of Ohio and nine other members of the House of Representatives signed the lawsuit challenging what they described as Obama's circumvention of Congress in authorizing the use of military force in a protracted effort to oust longtime Libyan ruler Moamer Kadhafi.

"With regard to the war in Libya, we believe that the law was violated. We have asked the courts to move to protect the American people from the results of these illegal policies," Kucinich said in a statement as the lawmakers filed their suit in a federal court in Washington.

The US Constitution stipulates that only Congress has the right to declare war.