Gunmen have launched an attack on the Radisson Blu Hotel in the centre of Mali's capital, Bamako.

"Apparently it's an attempt to take hostages. The police are there and are sealing off the area," a security source told Reuters news agency.

Automatic weapon fire could be heard from outside the 190-room hotel, AFP reports.

BBC Afrique's Abdourahmane Dia says the US-owned hotel is popular with expats working in Mali.

In August, suspected Islamist gunmen killed 13 people, including five UN workers, during a hostage siege at a hotel in the central Malian town of Sevare.

France, the former colonial power in Mali, intervened in the country after al-Qaeda-linked militants threatened to march on Bamako in January 2013 after taking control of the north of the country.

Mali attack: Live updates

The US embassy in Bamako has tweeted that it "is aware of an ongoing active shooter operation at the Radisson Hotel".

All US citizens were asked "to shelter in place" and "encouraged to contact their families".

"It's all happening on the seventh floor, jihadists are firing in the corridor," a security source told AFP.

Witnesses say the police have surrounded the hotel and are blocking roads leading into the neighbourhood.

The Rezidor Hotel Group, which owns the Radisson Blu, said it was aware of "the hostage-taking that is ongoing at the property today".

"As per our information two persons have locked in 140 guests and 30 employees," AFP quotes its statement as saying.

The UN force in Mali took over responsibility for security in the country from French troops in July 2013.

Militancy in Mali

October 2011: Ethnic Tuaregs launch rebellion after returning with arms from Libya
March 2012: Army coup over government's handling of rebellion, a month later Tuareg and al-Qaeda-linked fighters seize control of north
June 2012: Islamist groups capture Timbuktu, Kidal and Gao from Tuaregs, start to destroy Muslim shrines and manuscripts and impose Sharia
January 2013: Islamist fighters capture a central town, raising fears they could reach Bamako. Mali requests French help
July 2013: UN force, now totalling about 12,000, takes over responsibility for securing the north after Islamists routed from towns
July 2014: France launches an operation in the Sahel to stem jihadist groups
Attacks continue in northern desert area, blamed on Tuareg and Islamist groups
2015: Terror attacks in the capital, Bamako, and central Mali

Two gunmen took 170 hostages during an attack on the Hotel Radisson in the Malian capital, Bamako, Agence France-Presse reported, citing the hotel group.

“The attack is ongoing,” United Nations spokesman Olivier Salgado said by phone from the capital. “What we know is that the attackers are in the hotel and have automatic weapons.”

UN forces and Malian government troops are at the scene, he said. The French and U.S. embassies confirmed that the attack was under way.

Mali was plunged into violence after a military coup in March 2012 left a power vacuum that allowed Islamist militants to join with separatists and seize northern areas of the country. While French and UN forces pushed the militants out of most of those strongholds in 2013, the government is struggling to regain authority there.