The Republican leader of the U.S. House of Representatives voiced support on Thursday for President Barack Obama's expanded campaign against Islamic State militants, but members of his party questioned whether the plan to rely mainly on airstrikes and arming Syrian rebels was forceful enough.

Obama sent a panel of top administration officials to the Capitol to make the case to the U.S. Congress for broadening operations against the Sunni militants, including U.S. air strikes in Syria for the first time and more military advisers in Iraq.

In a televised address on Wednesday night, the Democratic president declared he would lead an alliance to root out Islamic State, plunging the United States into two conflicts in which nearly every country in the Middle East has a stake.