A top White House official said Monday residents of the Florida Keys may not be able to return to their homes for several weeks, and said the federal government will need more time to assess the damage done to roads and bridges there by Hurricane Irma.

"The Keys are going to take awhile," Tom Bossert, White House homeland security adviser, said during Monday's White House press briefing. "We have not assessed the structural integrity of the bridges there."

Bossert said there is reason to believe some of the drawbridges lifted during the storm may have been bent, and restoring them is "going to take some time."

"I would expect that the Keys are not fit for re-entry for regular citizenry for weeks, and if that's wrong and I'm wrong then fine, then let the local officials bring you in," he said. "But I would set that expectation pretty broad right now."

Hurricane Irma made landfall in South Florida over the weekend, and was downgraded to a tropical storm Monday. The Florida Keys was under a mandatory evacuation order before the storm hit Saturday.