Investigators have uncovered no signs of U.S.-based terrorists linked to a plot to blow up airliners headed to the United States, Homeland Security Secretary Michael Chertoff said Friday.

"Currently, we do not have evidence that there was, as part of this plot, any plan to initiate activity inside the United States or that the plotting was done in the United States," Chertoff said, a day after British authorities announced the arrests of two dozen suspects.

The arrests led the Bush administration to put the U.S. on its highest threat alert on flights headed to the United States from the United Kingdom. Additionally, all other flights were raised to the second-highest alert level.

Click here for more FOX News coverage of the airline terror plot.

But Friday, Chertoff said his department was looking to adjust some of the new traveling restrictions — they have barred many common carry-on items such as water bottles and toiletries — to "somewhat reduce any additional inconvenience." He provided no details.

"I don't want to suggest that they're going to be earth- shattering, but we're going to move to try to make this as simple and as easy as possible, as quickly as possible," he said in a news conference at Reagan National Airport.

Even so, Chertoff cited the possibility of other terrorists or sympathizers, saying, "So I'm not prepared to let my guard down."

He said that over the longer term, officials would examine the threat involved in this week's plot — some common chemicals, which combined can form a deadly explosives.

Officials will study "how we can calibrate our systems to take account of these developments, and then, with that in mind, try to ultimately come back to a regime of security that will give the maximum amount of freedom to the travelers," he said.