The top Senate Republican said on Thursday President Barack Obama can expect bipartisan support in Congress if he offers a "credible plan" to go after Islamic State militants, as senior US officials prepare to brief lawmakers on the matter.

Some lawmakers contend that Obama should seek congressional authorization for airstrikes in Iraq against the Sunni militants.  However, it is not clear whether such a vote would take place this month or whether he needs Congress to approve the limited actions already under way.

Obama "needs to come forward with a plan" for dealing with the Islamic State, Senate Republican leader Mitch McConnell told Reuters in an interview in Kentucky, where is campaigning for re-election.

"I think the Congress is anxious to see what the president thinks we ought to do about this," McConnell said.

"My guess is it will require some kind of authorization from us, maybe some kind of funding, and I think if it's a credible plan to go after these killers, he's very likely to be supported on a bipartisan basis," added McConnell, a fierce critic of Obama.

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