(CNN) -- Amid international concerns about security, the Sochi Games completed the first day of contests Thursday with high excitement and -- equally important -- no major adverse incident.

After all the anxiety about a terror strike, controversy over gay rights and ridicule over poor preparations, the Winter Olympics commenced smoothly enough, as qualification events were held in the men's and women's slopestyle, women's moguls and team figure skating.

The last of the athletes arrived at the Russian venue on Thursday, including the bulk of Team USA, and the Olympians will hold the Games' official opening ceremony Friday.

On the eve of that ceremony, Dmitry Chernyshenko, head of the Games, promised Sochi will be "the safest place on Earth during the Olympics."

Thursday's developments involved more than just sports.

SECURITY

There's no doubt it's the issue at the forefront of people's minds.

Russia has drafted some 37,000 police and security officers to handle security in Sochi. But that's not been enough to assuage everyone's fears.

Toothpaste terror: A day after the United States warned of how explosive materials could be concealed in toothpaste or cosmetic tubes, its government Thursday temporarily banned all liquids, gels, aerosols and powders in carry-on luggage on flights between the United States and Russia.

A law enforcement source told CNN the effort is intended as a very targeted response to the threat that became public Wednesday, and should have a minimal impact on the traveling public. The Transportation Security Administration ordered airlines to ban the items from carry-on bags, but allow them in checked bags.

U.S. partnership: Meanwhile, U.S. authorities are working with the Russians and other countries to try to disrupt several possible threats, including the toothpaste tube concern, a U.S. intelligence source said Thursday.

The threats vary in credibility, and the biggest one traces to the group Imarat Kavkaz in Russia, which has publicly said its followers will try to disrupt the games, the official said.

Meanwhile, Sen. Dianne Feinstein, D-California, told CNN she's read the threat reports about the Olympics. "The threat stream is credible, I think it's real," she said.

Feinstein noted at least one terrorist group -- the Caucasus Emirate -- "is conceivably capable of carrying out an attack," she said.

"If I had a son or daughter performing in the Olympics, I would go. Now that I don't, I probably would not," said Feinstein. "I've seen the threat stream, and I know the opposition, and the opposition is dogged. It is continuing, it is threatening, and hopefully arrests can be made and any attack can be stopped."

Private protection: The U.S. ski and snowboarding team has hired a private security firm, Global Rescue, to provide protection. It's not clear how much the firm could do in the event of a major incident, when Russian forces will be in charge, but it has been gathering intelligence on the ground and will provide an extra layer of protection as athletes travel around.

Ships for safety: Meanwhile, two U.S. Navy ships have steamed into the Black Sea, where they will be ready to help if any mass evacuation of U.S. citizens is needed. U.S. security officials have also been working with their Russian counterparts on how to keep the Games safe against the backdrop of a regional separatist movement that has used terrorism in the past and has threatened to use it during Sochi's Olympic Games.

Targets of threats: Americans are not the only ones who are jittery. Austria said this week that two of its female athletes had been the target of specific threats. Austrian media reported an anonymous letter was sent warning Alpine skier Bernadette Schild and skeleton racer Janine Flock they could be kidnapped.

We've heard it before: It's not the first time security issues have dominated the build-up to the Olympics -- Britain parked missile batteries on apartment block roofs and a warship on the River Thames before the 2012 Games. The Salt Lake City Winter Olympics in 2002 were held amid heightened security only months after the 9/11 terror attacks in the United States -- and the 1996 Summer Games in Atlanta were subject to a terror attack.

Being an athlete: Upon arriving to Sochi, U.S. ice skater Maia Shibutani didn't hear of the explosive toothpaste threat. She and brother Alex, her skating partner, had been too busy traveling.

But she can't be distracted by the threats, as serious as they are, she said.

"Yesterday we were doing processing, and then we were traveling all morning, so, no, we hadn't heard about that," she said Thursday of the toothpaste threats. "But I think that, really our job here is to just focus on what we can control and what we can do, and that's how we're going to perform at our first Olympics."

Is Sochi ready?

PREPARATIONS

When Russia bid to host its first Winter Olympics in 2007, a document quoted an expected cost of around $12 billion. That figure has ballooned to around $50 billion. That's more than four times over budget and surpasses Beijing's 2008 Summer Games -- making it the most expensive Olympics ever, summer or winter.

Russia had less than seven years to transform what was a fairly low-key seaside resort town into a Winter Olympics venue -- a project that required staggering feats of engineering in building a new freeway and rail link up a mountain, and a ski resort on the top. And yet questions over Sochi's readiness have dogged the final run-up to the Games.

Not quite there: While the sports facilities were completed in good time, journalists and others arrived in Sochi this week to find that some of the 40,000 new hotel rooms were far from ready and that construction workers were still hard at work on parts of the Olympic Park.

Thanks to pictures of chaotic scenes posted on Twitter, Russia's pride has not been spared.

But CNN's Ben Wyatt in Sochi reports that the picture is not all bad. His hotel has been "superb" and staff and Games volunteers are clearly making an effort to be helpful and speak English, he said.

While some media hotels and landscaping projects have not been completed on time, the sporting venues are all looking in very good condition, he said.

It'll be A-OK: The Games are President Vladimir Putin's pet project -- so the pressure is on for the Russian organizers to deliver and foster the country's reputation as a wealthy, modern state.

Chernyshenko, head of the Games, told CNN he was confident all was in hand ahead of Friday's opening ceremony.

"We are pretty sure that the minor issues are fixed," he said. "And everybody will concentrate on sport and excellence."

PROTESTS

Every Olympics has protests. But thanks to social media, Russia is facing a global backlash.

What got many people riled was Russian lawmakers' passage last summer of legislation known as the anti-gay propaganda bill. The law makes it illegal to tell children about gay equality.

Open letter: More than 200 writers from around the world signed an open letter published Thursday in the UK newspaper The Guardian, calling for a repeal of laws that have placed a "chokehold" on the right to free expression in Russia.

"As writers and artists, we cannot stand quietly by as we watch our fellow writers and journalists pressed into silence or risking prosecution and often drastic punishment for the mere act of communicating their thoughts," the letter said. Authors Salman Rushdie, Jonathan Franzen and Nobel laureates Gunter Grass and Orhan Pamuk are among the signatories.

First athlete to protest?: Russian state-run media agency RIA Novosti reported that Russian athlete Alexei Sobolev sported an image on his snowboard resembling "a female figure in a balaclava wielding a knife."

That image purports to resemble members of Pussy Riot because the anti-Putin, all-female band perform while wearing balaclavas, headgear that shows only part of the face, the news agency reported.

The headline stated: "Sochi Snowboarder Coy on Possible Pussy Riot Protest." Three band members were sentenced to prison for performing a song critical of Putin in one of the Russian Orthodox Church's most important cathedrals in February 2012. Band supporters say the musicians were political prisoners.

When asked whether the design was an homage to Pussy Riot, Sobolev responded: "Anything is possible." He added: "I wasn't the designer."

Sobolev, a slopestyle rider, was the first Russian to compete in the Games and finished 10th in a qualifying heat Thursday. The drawing on his snowboard was described as "what could be the first protest by an athlete" in the games, the Russian news agency said.

Coordinated protests: To keep the issue in the public eye, gay rights group All Out coordinated protests in cities around the world Wednesday -- New York, London, Rio de Janeiro and Paris among them. It's also set up the Principle 6 campaign, named for the article in the Olympic Charter that promises no discrimination.

Designated site: There is a designated protest site in Sochi. But there's been criticism of organizers' decision to tuck it away in a hard-to-reach village seven miles from the main Olympic Park.

More protests may be yet to come -- perhaps even by athletes despite an Olympic Charter rule that states: "No kind of demonstration or political, religious or racial propaganda is permitted in any Olympic sites, venues or other areas."

Express yourself: Chernyshenko says visitors to Sochi have nothing to fear. "You have to understand that any discrimination by gender, by sexual orientation, or religious is prohibited in my country by constitution and also by Olympic Charter.

"Athletes are free to express themselves, and for those who want to demonstrate something we organized what we call Sochi 'speakers' corner.' "

EVENTS

Athletes strapped on their skis, snowboards and ice skates Thursday as the sporting spectacle got under way.

All together now: U.N. Secretary-General Ban Ki-moon urged warring leaders to take a leaf from the competitors' book. "The athletes send a unified message that people and nations can put aside their differences. If they can do that in Sochi's sporting arenas, leaders of fighters should do the same in the world's combat areas," he said Thursday.

Making the cut: Qualification rounds began for the women's moguls, and figure skaters took the ice for the team men short program and the team pairs short program.

The qualification rounds in the men's and women's slopestyle competition -- making its debut at the Sochi Games -- saw athletes whiz down a daunting course littered with bumps, rails and jumps.

Thanks, I'll pass: The aforementioned event is the one ditched by champion U.S. snowboarder and skateboarder Shaun White.

The king of cool, who's been nursing a wrist injury, withdrew Wednesday, a day after admitting the slopestyle course presented an "intimidating" challenge. He's going to focus instead on winning his third gold medal in the halfpipe, another snowboarding event.

Record numbers, record tally?: Team USA, with 230 members, will be the largest athlete delegation for any nation in Winter Olympics history. Made up of 125 men and 105 women, the team has high hopes of bringing back a record tally of medals.

9 ways Sochi surprises

CNN's Amanda Davies, Zain Asher, Carol Jordan, Michael Martinez, Jake Tapper, Evan Perez and Paul Cruickshank contributed to this report.