Competition in the Sochi 2014 Winter Olympics officially began on Thursday, 32 hours before the opening ceremony. Early starts are needed because of 12 men's and women's medal events added since the 2010 Vancouver Olympics.
Even though Russian President Vladimir Putin declared the country was "ready", questions remain over Russia's suitability as a venue for the 18-day-long event amid concerns over terror threats and gay rights issues.
There has been a sense of uneasiness surrounding those headed for Sochi, with bombings in Volgograd and reports of suicide bombers readying themselves for operation during the Games in the recent months.
Meanwhile, UN Secretary General Ban Ki-moon condemned attacks and discrimination against homosexuals on Thursday, touching on the gay rights issue in Russia that has overshadowed preparations for the 22nd Winter Olympics.
Openly gay tennis legend Billie Jean King has withdrawn from the US presidential delegation to the Games, citing the ill-health of her mother.
"Many professional athletes, gay and straight, are speaking out against prejudice," Ban told a session of the International Olympic Committee in Sochi in a keynote address.
"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," he added.
Ban did not specifically address the situation in Russia, where Parliament passed a hugely controversial law last year banning the dissemination of "gay propaganda" to minors.
Activists see the law as virulently homophobic and it led to calls in some quarters for a boycott of the Sochi Games.
Worse, the United States has reportedly warned American and foreign airlines that militants could try to hide explosives in toothpaste tubes on Russia-bound flights.
An official told AFP it has information "specifically targeting flights to Russia".
In a statement, the department of homeland security said it was not aware of any specific threat, but added "as always, our security apparatus includes a number of measures, both seen and unseen".
Suicide bombings in the southern Russian city of Volgograd in late December killed 34 people and raised fresh concerns about the ability of the Russian authorities to ensure security during the Games, taking place close to Russia's restive Northern Caucasus region.
Russian security forces are still fighting Islamist insurgents in the Northern Caucasus and militants have threatened to strike targets in Russia during the Games.
About 40,000 members of the Russian security forces are on duty in an around Sochi during the Games in one of the tightest operations ever mounted at an Olympics.
The Games are the biggest event that Russia has hosted since the fall of the Soviet Union and the project has been championed by Putin ever since the successful bid in 2007.
Friday's opening ceremony will be attended by more than 40 heads of states including Chinese President Xi Jinping and embattled Ukrainian President Viktor Yanukovych, who is facing protests at home.
But no major Western leader is expected in what many see as a snub to Russia over its rights climate.
(With inputs from AP and AFP)