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Terrorists armed with bombs and guns launched an attack on a Libyan hotel popular with leaders and Western diplomats Tuesday, killing several people including at least one American.

Guests fled the waterfront Corinthia Hotel in Tripoli when the attack began shortly after 9 a.m. local time (2 a.m. ET). A car bomb later exploded outside, sending black smoke into the sky.

"It is more than likely that there are hostages held by the gunmen on the 23rd floor," Essam Naas, a spokesman for Tripoli security forces, told Reuters. "The security forces are evacuating the guests floor by floor. There was shooting between the gunmen and the security forces."

However, Mahmoud Hamza, commander of Libya’s Special Deterrent Force, told private satellite television station al-Nabaa that the situation was "under control," though he couldn't confirm the whereabouts of the gunmen.

#Libya | UPDATE (unconfirmed): #IslamicState claims that its fighters are now engaged in a shootout inside Corenthia pic.twitter.com/Yupulecom1 — Good Morning Libya (@Morning_LY) January 27, 2015

Five foreigners were killed inside the hotel, The Associated Press quoted Hamza as saying.

NBC News could not immediately confirm that report, but later Tuesday, a Virginia-based security training and operation firm said one of its employees, David Berry, died in the attack. "Our company mourns this extraordinary loss with his family and friends," Cliff Taylor, chief operating officer of Team Crucible LLC, said in a statement.

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A senior State Department official confirmed a U.S. citizen was among the dead.

A hotel worker told the AP that there were five masked attackers and they had fired randomly at the staff in the lobby. The staffer, who did not want to be identified, said Italian, British and Turkish guests were staying at the hotel but that it was largely empty when the attack occurred.

The worker said colleagues and foreign guests fled out the hotel's back doors into the parking lot. When they got there, he said a car bomb exploded only 100 yards away.

The hotel, part of the Malta-based Corinthia chain, is popular with diplomats and lawmakers from Libya’s chaotic rival governing factions. Former Prime Minister Ali Zeidan lived there when militia kidnapped him in 2013.

The area around the scene was sealed off by people wearing police uniforms.

#Libya | More photos of today's double suicide car bombing outside #Tripoli's Corenthia hotel: pic.twitter.com/GBWLo5pwi8 — Good Morning Libya (@Morning_LY) January 27, 2015

It was not immediately clear who was behind the attack but the SITE monitoring service reported a militant group claiming affiliation with ISIS had claimed responsibility, adding that it was in revenge for the recent death in custody of Abu Anas al-Libi. Al-Libi, 50, was alleged to have helped plan the 1998 bombings of U.S. embassies in Tanzania and Kenya. He died in New York while awaiting trial earlier this month.

However, local security sources said the target of the attack was most likely Omar al-Hasi, the prime minister of one of two rival governments competing for control of the country. Al-Hasi was living in the hotel.

The U.S. State Department was “closely tracking” the attack and said the U.S. had a “firm” commitment to United Nations’ efforts to “build an inclusive system of government,” agency spokeswoman, Jen Psaki said Tuesday.

"Violence will not resolve Libya's problems and this attack cannot be allowed to impede the critical work that is underway to find a political solution," she said.

Malta Today published security images of what it said were the suspected attackers. NBC News could not immediately verify the report.

Malta’s Prime Minister Joseph Muscat said on Twitter that all Maltese citizens at Corinthia were “currently in a safe location.”

Confirmed that all Maltese at Corinthia Tripoli are currently in a safe location. Continuing to follow events closely with hotel operators. — Joseph Muscat (@JosephMuscat_JM) January 27, 2015

Matthew Dixon, commercial director of the Corinthia Hotel Group, said: “The situation is unfolding in front of us. We have no further information above and beyond what is being reported locally.

“At the moment we have not had contact with the hotel abut we’re monitoring the situation here and from our headquarters in Malta.”

Giuma Bukleb, a spokesman for the Libyan Embassy in London, said he did not have any information about the nationality of the hostages or the attack itself.

NBC News' Miranda Leitsinger, Reuters and The Associated Press contributed to this report.