Reports from Mali indicate 170 people have been taken hostage in a luxury hotel in the Malian capital Bamako on Friday.
"The Rezidor hotel group, which manages the Radisson Bluhotel in Bamako, understands that a hostage-taking is under way at the site today," the group said in a statement quoted by the BBC.
"According to our information, two people are holding 140 clients and 30 employees".
The raid on the Radisson Blu hotel, which lies just west of the city center near government ministries and diplomatic offices in the former French colony, comes a week after Islamic State (IS) militants killed 129 people in Paris.
The identity of the Bamako gunmen, or the group to which they belong, is not known.
Northern Mali was occupied by Islamist fighters, some with links to al Qaeda, for most of 2012. Although they were driven out by a French-led military operation, sporadic violence has continued.
The security source said as many as 10 gunmen had stormed the building, firing shots and shouting "Allahu Akbar", or "God is great" in Arabic.