US authorities announced a temporary ban Thursday preventing travelers from bringing any liquids, gels or aerosols aboard Russia-bound flights amid a security threat to the upcoming Winter Games.

The US Transportation Security Administration directive came a day after Washington warned American and foreign airlines that extremists may place explosive materials in toothpaste or cosmetic tubes in an attempt to disrupt the Olympics in the Russian resort of Sochi.

The banned items, however, can be placed in customers' checked baggage. Prescription medications are allowed.

Stringent rules about liquids and toothpaste in hand luggage have been standard practice on US carriers after a string of thwarted bomb plots in the years following the September 11, 2001, attacks.

But until now, limited amounts were allowed on board.

"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," a Department of Homeland Security official said.

"These measures include intelligence gathering and analysis, deployment of cutting edge technology, random canine team searches at airports, federal air marshals, federal flight deck officers, temporarily restricting certain items and more security measures both visible and invisible to the public."

Delta Airlines said on its website that customers traveling between the two countries would have to check in with an airline agent at the airport, not online, their smartphones or at airport kiosks.

"Delta encourages customers traveling to and from Russia to arrive at the airport at least two hours in advance of departure time," the airline said.

Concerns over security at the Games, which open on Friday, skyrocketed after two suicide attacks that killed 34 people in the southern Russian city of Volgograd in December, blamed on extremist militants from the Northern Caucasus region.

Russian security forces are still fighting insurgents in the Northern Caucasus region, which is close to Sochi, and militants have threatened to strike targets in Russia during the Olympics.

About 40,000 members of the Russian security forces are on duty in and around Sochi in one of the tightest operations ever mounted at an Olympics.

Two US warships have arrived in the Black Sea and will stand ready to offer assistance in the case of a security emergency, including the evacuation of Americans in the event of an attack.

[Image via Agence France-Presse]