Briefing US lawmakers in Washington, senior generals said the US-led anti-IS coalition was working with local ground forces to isolate the group's Syrian stronghold in the city of Raqa.
But General Joseph Votel, head of Special Operations Command, said this broad strategy does not yet amount to a plan to storm Raqa, despite recent advances by US-backed fighters grouped under the "Syrian Democratic Forces" banner.
"There is currently not a plan," he said.
Asked whether the coalition has a plan to hold the city after it falls, he added: "I would say no, there is not a plan to hold Raqa."
General Joe Dunford, who is the US military's highest-ranking officer, later told reporters that any move to retake Raqa would be contingent on a variety of factors.
"We don’t have a timeline along which I would tell you that I know we are going to retake Raqa," he said during a work trip to Florida.
Signup to our newsletter and follow us on Facebook and Twitter!
"It's going to be conditions-based. It will be based on the size of the force... it will be based on enemy disposition."
Dunford pointed to recent gains in and around the town of Shadadi, which US-supported local forces recaptured from the IS group last month, as evidence of momentum for an eventual recapture of Raqa.
"This is all part of tightening the noose on ISIL in Syria," he said.
General Lloyd Austin, who currently heads the US military's Central Command, which manages Middle East operations, told lawmakers it might be time to revisit a contentious program to train and equip groups of Syrian fighters to hold recaptured territory.
"I've asked for permission to restart the effort by using a different approach," Austin said, adding the revived program would focus on training smaller numbers of fighters.
The program attracted scorn after it emerged some trainees had given gear and ammunition to an Al-Qaeda-linked affiliate, the Al-Nusra Front.
Votel also faced questions from the Senate Armed Services Committee on the composition of the SDF units that the US-led coalition relies upon for ground operations in the Raqa area.
He said the group is "probably about 80 percent" Kurdish. The US-led coalition has been criticized for its overreliance on Kurdish allies, who may struggle to win over civilians in a mainly Arab town like Raqa and are considered suspect by neighboring Turkey.