French police have lost contact with a 24-year-old gunman suspected of killing seven people in the name of al Qaeda and there has been no sign of life from his apartment in southwestern France for 10 hours.
Mohamed Merah has confessed to killing three soldiers, three Jewish children and a rabbi.
It is more than a day since 300 police first surrounded the five-storey building where he lives in a suburb of Toulouse.
Interior Minister Claude Gueant said two shots had been heard during the night.
Merah, a French citizen of Algerian origin, has told negotiators that he killed the seven to avenge the deaths of Palestinian children and because of French army involvement in Afghanistan.
Earlier explosions were heard at the building where the suspect is holed up, but an official said police had not launched an assault.
An interior ministry official said the blasts were part of moves to intimidate the man who had changed his mind and did not want to surrender.
Police have been trying to get Mohamed Merah to turn himself in since he fired through the door at them while they tried to storm his apartment in the suburbs of Toulouse in the early hours of Wednesday morning.
The shootings began on 11 March with the death of a soldier, and, days later, two more soldiers were shot and killed.
Earlier this week, three children and an adult were shot and killed outside a Jewish school.
Anti-terror chief Francois Molins said the suspect had planned more killings, of a soldier and two police officers.
Three children and a rabbi whom the suspect is alleged to have killed at the school have been buried in Jerusalem.
French Foreign Minister Alain Juppe accompanied the bodies on the flight to Israel.