In Paris, French President Emmanuel Macron is closely following developments of the attack on a hotel resort in Mali's capital where suspected jihadists took hostages in a spot popular with foreigners.
"The U.S. Embassy informs U.S. citizens of a possible increased threat of attacks against Western diplomatic missions, places of worship, and other locations in Bamako where Westerners frequent".
Religious extremism in Mali once was limited to northern areas, although in recent years the jihadists have spread violence farther south, including a devastating attack on the Radisson Blu hotel in Bamako in November 2015. "Malian special forces intervened and about 20 hostages have been released", Security Minister Salif Traore told AFP.
Security has gradually worsened in Mali since French forces pushed back allied Islamist and Tuareg rebel fighters in 2013 from swathes of the north they had occupied the previous year.
The UN official said those at the resort when the attack began included people affiliated with the French military mission as well as the UN and European Union missions in the country.
This breaking news story is being updated and more details will be published shortly.
Sunday's attack is the latest in a series of high-profile assaults in north and and west Africa targeting locals and tourists.
But jihadists have continued to mount numerous attacks on civilians and the army, as well as on French and United Nations forces still stationed there.
Malian soldiers and troops from France's Bakhane counter-terrorist team have arrived at the scene.
Andrea de Georgio, a freelance journalist in Bamako, also quoted officials as saying that at least two people were killed.
It has been targeted constantly by jihadists, with dozens of peacekeepers killed, including five on Saturday.