By Patricia Zengerle
WASHINGTON (Reuters) - Republican Senator Rand Paul called on Congress on Wednesday to formally declare war on Islamic State, as debate intensified in the Senate and House of Representatives over the campaign in Iraq and Syria.
The Kentucky senator introduced a Senate resolution seeking to declare that a state of war exists with the militant group, the target of four months of air strikes by U.S. and allied forces.
"Right now, this war is illegal until Congress acts pursuant to the Constitution and authorizes it," Paul, a likely 2016 presidential contender, said in a statement.
Lawmakers will vote in the coming days on a sweeping defense spending bill, the National Defense Authorization Act, which among other things authorizes the arming of moderate Syrian rebels as part of the Islamic State fight.
Paul's resolution is unlikely to be brought up for a vote any time soon.
Most lawmakers do not favor a formal declaration of war, saying the campaign is not that extensive.
But many, including Republicans and Obama's fellow Democrats, want to debate and vote on a formal authorization for the use of force setting guidelines for the fight against the Sunni militants, who have killed thousands of people while seizing swaths of territory in Iraq and Syria.
Senator Tim Kaine, a Virginia Democrat, said there is a "strange conspiracy of silence" about a "unilateral war" that has already cost U.S. taxpayers more than $1 billion. He called on Obama to engage with Congress on the issue and urged lawmakers not to head home this month without a vote.
"We owe it to our troops serving abroad, troops who are engaged in war even as we think about recessing and leaving Washington on Dec. 11 for the holidays, to do our job and to have a debate and vote about the war that our Constitution demands," Kaine said in a Senate speech.
(Reporting by Patricia Zengerle; Editing by Steve Orlofsky)