The blasts were filmed by journalists broadcasting near the suspected gunman's home
The police siege of a building in the southern French city of Toulouse, where a man suspected of killing seven people is holed up, has entered a second day.
Late on Wednesday gunfire and at least one explosion were heard at the block of flats in the north of the city.
Earlier, three more blasts were heard, accompanied by flashes of orange light.
Mohammed Merah, 23, is suspected of killing four people at a Jewish school last Monday and three soldiers in two attacks last week.
The earlier blasts sent shockwaves around the quiet residential streets around the building, reports the BBC's Christian Fraser in Toulouse.
After the first explosions, deputy mayor, Jean-Pierre Havrin told local media that "negotiations have finished and the assault has begun".
However, sources from the French interior ministry were later quoted as saying said this was only the beginning of an operation to put pressure on Merah.
"They [the blasts] were moves to intimidate the gunman who seems to have changed his mind and does not want to surrender," interior ministry spokesman, Pierre-Henry Brandet told Reuters.
Police had been negotiating with Merah but had not convinced him to surrender.
Police surrounded Merah's block after two officers were shot at when they tried to get into his flat early on Wednesday morning.
Officials say he is heavily armed with a Kalashnikov high-velocity rifle, a mini-Uzi 9mm machine pistol, several handguns and possibly grenades.
Street lights had been switched off in the vicinity of the building on Wednesday evening.
The five-storey block of flats has been evacuated, and police also moved residents from nearby buildings.
Elsewhere in the city, police are hunting for accomplices and have detained several members of Merah's family.
His mother was taken to the scene on Wednesday in the hope that she could persuade him to surrender, but she told police that she had no influence over her son.