As Russian forces crossed the border into Ukraine's Crimean peninsula over the weekend, Secretary of Defense Chuck Hagel said the situation there risked becoming dangerously unstable.

"This could be a very dangerous situation if this continues in a very provocative way," Hagel said in an interview, recorded Friday, with CBS's Face the Nation. "We have many options, like any nations do. We're trying to deal with the diplomatic focus. That's the appropriate responsible approach and that's what we're going to continue."

Hagel's prerecorded remarks came before the Russian parliament on Saturday unanimously voted to send troops into Ukraine. Responding to that action, Secretary of State John Kerry called on Russia to withdraw its troops, warning that it could face stiff sanctions from the international community if it failed to do so.

Samuel Sam-Sumana, vice president of Sierra Leone, announced on Saturday that he would "lead by example," and spend 21 days in voluntary quarantine, following the death of his bodyguard from Ebola last week, BBC News reports.

While the number of reported cases in Sierra Leone had been on the decline, a recent uptick was cause for concern, according to government officials. More than 23,500 Ebola cases have been reported in Sierra Leone, Liberia, and Guinea since the outbreak began in December 2013; nearly 10,000 people have died from the disease.

Carrying signs declaring "I am not afraid," and portraits of murdered Russian politician Boris Nemtsov, thousands marched through Moscow on Sunday, Reuters reports.

(AP Photo/Dmitry Lovetsky)

The demonstrators walked in honor of Nemtsov, who was shot four times on Friday while walking across a bridge near the Kremlin. The harsh critic of Russian President Vladimir Putin had served as deputy prime minister under Russia's first post-Soviet President, Boris Yeltsin, in the 1990s. He became a popular figure in opposition politics after Yeltsin's successor, Putin, came to power.

(AP Photo/Pavel Golovkin)

"If we can stop the campaign of hate that's being directed at the opposition, then we have a chance to change Russia," Gennady Gudkov, an opposition leader, told Reuters before the march. "If not, then we face the prospect of mass civil conflict."

(AP Photo/Pavel Golovkin)

Putin has condemned Nemtsov’s murder as a "provocation," and Kremlin investigators say they are pursuing several leads. In interviews before his death, Nemtsov said he feared Putin might want him dead because of his involvement with the opposition.

Ronda Rousey needed just 14 seconds on Saturday night to defend her UFC bantamweight title against Cat Zingano, ESPN reports.

It was Rousey's (11-0) fifth UFC title defense; her last three have lasted just 66 seconds, 16 seconds, and now 14 seconds — the latter being the fastest finish of her career thus far and a UFC record for fastest ever in a title fight.

Rousey submitted Zingano with a straight armlock after Zingano rushed Rousey on the opening bell; Zingano quickly tapped out of the hold.

Venezuelan President Nicolas Maduro condemned what he says are moves by the United States to unseat him at a rally on Saturday, Reuters reports.

"We have captured some U.S. citizens in undercover activities, espionage, trying to win over people in towns along the Venezuelan coast," Maduro said. "In Tachira, we captured a pilot of a U.S. plane (who is) of Latin origin (carrying) all kinds of documentation."

A U.S. embassy spokesman in Caracas declined to comment on Maduro's statements, saying that there had not been any official, diplomatic communication on the charges with the Venezuelan government. But an Obama administration official dismissed the accusations, calling them "baseless and false."

Maduro also said he would institute visa fees for Americans who want to enter Venezeula, reduce the number of U.S. embassy officials allowed in Caracas, and bar certain U.S. citizens from entering the country, including former President George W. Bush and former Vice President Dick Cheney.

Rand Paul may have been feeling a bit of good deja vu on Saturday — the Kentucky senator won the straw poll yet again at Saturday's Conservative Political Action Conference, The Washington Post reports.

Gov. Scott Walker (R-Wis.) finished just behind Paul in second place, in the last round of CPAC nods before primary voting for the 2016 presidential election begins. While Paul entered the weekend event as the prohibitive favorite in this year's balloting, his percentage of the vote actually dropped, from 31 percent in 2014 to 25.7 percent in 2015.

Voting attendees increased by nearly 20 percent from 2014, but organizers were quick to note that the results show “how fluid and open the race is.”

Silence is golden, according to the World Health Organization.

WHO figures say 43 million people ages 12-35 have suffered hearing loss, and another 1.1 billion teenagers and young adults risk damaging their hearing. The culprit? Listening to music "too much, too loudly," BBC News reports. 

And it's not just your laptop or office earbuds that could be doing damage. WHO warns that concerts and bars are a "serious threat" as they too expose people to unsafe sound levels. The organization recommends taking "listening breaks" if you must frequent such venues, and limiting daily music listening to one hour, max.

Twelve years after thousands of artifacts were looted in the aftermath of the U.S.-led invasion, Iraq's national museum in Baghdad reopened on Saturday, The Washington Post reports.

Iraqi officials have worked for more than a decade to recover some 15,000 stolen artifacts. So far, about 4,300 pieces have been recovered.

The grand reopening was moved up, Prime Minister Haider al-Abadi said, as a message of defiance to Islamic State militants. Recent video showed purported ISIS members breaking statues at a museum in Mosul.

"Our hearts were broken when those artifacts were broken in Mosul," said Qassim Sudani, a spokesman for the Ministry of Tourism and Antiquities. "Now the national museum has reopened, it will be a lung that allows the Iraqi people to breathe again."

For sale: Hell.

A small town in Michigan that bears the name is on the market to the highest bidder, as unofficial Mayor of Hell John Colone put his holdings up for sale for the low price of $999,666, The Huffington Post reports.

While living in Michigan, I of course visited Hell, and I can tell you: There's not much there. But, if you have a million bucks lying around and love the idea of owning Hell's souvenir shop, ice cream store, weather station, post office, and other holdings, then hey, go for it.

You may have some competition from DAMNED, though, a Detroit-based artist group that launched a Kickstarter campaign to raise enough money to buy Hell. DAMNED wants to build a performing arts center, and if you contribute, the group is offering such perks as your own, personalized parking space in Hell. Sold!

President Abdel Fattah al-Sisi's administration continued its crackdown on Islamist groups on Saturday, as an Egyptian court declared the Muslim Brotherhood-offshoot Hamas a "terrorist" organization, Al Jazeera English reports.

A senior Palestinian official called the verdict "very unwise."

"Hamas is part of the Palestinian national unity movement," Mustafa Barghouti, who is neither from Hamas or Fatah, told Al Jazeera. "This decision is not useful."

The verdict stemmed from two private suits filed by attorneys against the Gaza Strip group, and came just days after Egypt implemented a strict new anti-terrorism law. Egyptian authorities outlawed the Muslim Brotherhood after the 2013 military coup, and they have since blamed Hamas for aiding rebel militants in Egypt — allegations Hamas denies.

Talk about a record you could do without.

Several Northeastern cities just suffered through the coldest February since reliable records began, NBC News reports. A slow-moving jet stream has funneled cold air down into the eastern United States, refusing to budge. On the ice block: Bangor, Maine; Syracuse, Buffalo, and Islip, New York; Hartford and Bridgeport, Connecticut.

"Usually these patterns last for a week or so. In this case it's been the whole month," Corey Bogel, a meteorologist for the National Weather Service, said.

And while forecasters say people can look forward to warmer-than-average months ahead, that's not the case quite yet: Sunday's low for Albany, New York is an even zero degrees.