WASHINGTON—The menu of options available to President Barack Obama in Iraq is a familiar one: Share intelligence, give tactical advice, launch airstrikes. But the president's decision is complicated by the difficult relationship with Baghdad since U.S. troops left and the amorphous nature of the enemy.

Mr. Obama said Friday that any U.S. action will take "several days" to begin and wouldn't include the deployment of American ground troops. The White House timetable drew a rebuke from some Republicans in Congress, who called for faster action.

Mr. Obama said he will consult with Congress but didn't say whether he would seek formal authorization from lawmakers, as he did when considering airstrikes against Syria last year.

"Iraq needs additional support to break the momentum of extremist groups and bolster the capabilities of Iraqi security forces," Mr. Obama said from the White House.

"People should not anticipate that this is something that's going to happen overnight," he said.