The deaths of seven people, including three young children, were being investigated Thursday in the southern French city of Nice as the result of a possible arson attack after a fire broke out in an apartment building overnight.

French prosecutors said they were looking into the possibility of arson after Nice Mayor Christian Estrosi said authorities had acquired images showing hooded people pouring a liquid into a stairwell in the building, CBS News partner network BBC News reported.

"I've asked the interior minister to deploy security forces to ensure residents' safety and avoid new incidents after this tragedy that's being investigated as potential arson," Estrosi said, according to Britain's The Standard newspaper.

The fire broke out on the second floor of the apartment building and then spread to the upper floors, BBC News reported.

Local media said all the people who died were from the same family. Officials identified the victims only as two adults, a teenager and a 10-year-old, a seven-year-old and a five-year-old, according to the BBC.

Two members of the family reportedly tried to escape through a window, but one died and the other was in critical condition on Thursday.