The U.S. Transportation Security Administration is temporarily banning carry-on liquids, aerosols, gels and powders on flights between Russia and the United States, a Department of Homeland Security official said on Thursday.

The items can be packed in checked luggage, said the official with the department, the TSA's parent agency. ABC originally reported the ban.

The United States issued a warning on Wednesday to airports and to some airlines flying to Russia for the Olympics to watch for toothpaste tubes that could hold ingredients to make a bomb on board a plane.

Russian forces are on high alert to head off possible militant attacks at the Winter Olympic Games, which begin on Friday in Sochi.

"As always, our security posture, which at all times includes a number of measures both seen and unseen, will continue to respond and appropriately adapt to protect the American people from an ever-evolving threat picture," said the DHS official, who spoke on condition of anonymity.

Restrictions, no mobile check-in

The safety measures include temporarily restricting some items, the official said.

U.S. Secretary of State John Kerry said in an interview with NBC News on Thursday that he was not aware of any specific threats tied to the Sochi games.

Kerry added that he would be comfortable if one of his daughters was flying to Russia to attend the Olympics.

"As I said, if an American wants to go, including my daughter, I'd say go," Kerry said.

A statement on Delta Air Lines Inc.'s website said prescription medicine would be allowed under the TSA directive. Travellers to Russia also need to check in personally with a Delta agent at the airport, and that online, kiosk and mobile check-in will not be available, it said.