Security concerns further clouded the run-up to the Olympics opening ceremony on Friday after the United States Transportation Security Administration said it was temporarily banning carry-on liquids, aerosols, gels and powders on non-stop flights between Russia and the United States.

The items will still be permitted on flights, a Department of Homeland Security official told news organization ABC, but could only be carried in checked luggage.

The ban follows a US warning to airports and airlines flying to Russia of the possibility that terrorists may seek to transport explosive-making material inside toothpaste tubes which could be detonated either during flights or at the actual games.

US and Russian security forces had been on high alert for possible terror threats in the weeks leading up to the games. Fears of attacks at the Olympics were raised in December when suicide bombers killed 34 people in the Russian city of Volgograd, 400 miles (700 km) northeast of Sochi.

Tens of thousands of Russian security forces were drafted in to prevent potential attacks ahead of the official opening of the games on Friday.

Countdown to colorful ceremony

The competition in Sochi began on Thursday, with qualifying underway in men's and women's snowboard slopestyling, women's freestyle moguls skiing and team figure skating events.

After a first downhill run, US alpine ski star Bode Miller and Norway's Kjetil Jansrud praised the downhill course.

"So far for us it's been great," Miller said.

Friday opening ceremony in the Black Sea resort's newly built Fisht Stadium will officially kick off the two-week extravaganza. Expected are 40 foreign heads of state, including China's President Xi Jinping and Japanese Prime Minister Shinzo Abe.

Noteable absentees will be US President Barack Obama, German Chancellor Angela Merkel and French President Francois Hollande.

Höfl-Riesch to carry German flag

Maria Höfl-Riesch has been chosen to carry the flag for Germany's 153-strong team at the ceremony. The 29-year-old alpine skier is considered one of her nation's best gold medal prospects in Sochi.

In total around 3,000 athletes, a record for the Winter Olympics, have gathered in Sochi to take part in 98 events.

World leaders shun opening ceremony

The Sochi Games may end up being more defined by the heads of state who have chosen to stay away to protest Russia's human rights record, including its stance on gay rights.

A law imposed in June 2013 which bans gay "propaganda" has been at the center of the controversy.

Ban highlights gay rights

Ban Ki-moon broached the subject in a speech to the International Olympic Committee on Thursday.

"Many professional athletes, gay and straight, are speaking out against prejudice," he said.

"We must all raise our voices against attacks on lesbians, gays, bisexual, transgender or intersex people. We must oppose the arrest, imprisonment and discriminatory restrictions they face."

Russian President Vladimir Putin has insisted that homosexuals will not be discriminated against during the Olympics.

ccp/lw (AFP, AP, dpa, Reuters)