French officials rejected charges that intelligence failures let a young man kill seven people, as the crack police unit that finally killed the gunman faced criticism of their operation.

Several security experts in Israel were scathing of the French police's handling of the siege, with one specialist calling it a disgrace AFP reported.

French investigators meanwhile were trying to establish whether Mohamed Merah, who murdered three Jewish children, a trainee rabbi and three soldiers in three separate attacks, had worked alone or with accomplices.

Prime Minister Francois Fillon said on Friday that security officials had known Merah, who died in a hail of police bullets, was a radical Islamist who visited Afghanistan.

But there was no reason to suspect he was planning attacks, he said.

The intelligence services "did their job perfectly well. They identified Mohamed Merah when he made his trips," he told French radio.

Intelligence agents "watched him long enough to come to the conclusion that there was no element, no indication, that this was a dangerous man who would one day pass from words to acts," said Fillon.

The head of France's DCRI domestic intelligence agency, Bernard Squarcini, told Le Monde newspaper there was little more that security services could have done to prevent Merah's atrocities.

Merah, 23, had claimed to be an Al-Qaeda member who killed to avenge Palestinian children and punish France for sending troops to Afghanistan.

An Al-Qaeda linked group, Jund al-Khilafah, claimed responsibility on jihadist websites for Merah's killings.

But Squarcini said Merah had not followed the usual path taken by Islamist extremists.

"According to statements he made during the siege, he self-radicalised in prison, on his own, reading the Koran," he said.

Merah had not been a member of any network, Squarcini added.

Merah had told police that when he travelled to Pakistan in 2011 he had not gone to the usual training centres, where spies might have reported his presence, he said. He said he had been trained by a single individual.

French agents had investigated Merah after his 2010 trip to Afghanistan, but had found none of the usual danger signs associated with organised extremism.

"No ideological activism, no visiting mosques," said Squarcini.

Merah died Thursday as he tried to shoot his way out of his apartment after a 32-hour police siege in the southwestern city of Toulouse.

French police unions reacted sharply Friday after a veteran police officer criticised what he said was a lack of clear tactics by the elite RAID unit that handled the siege and assault at Merah's appartment.

Christian Prouteau, who founded the GIGN, another elite unit drawn from the national police's rivals in the gendarmerie, said if they had used tear gas against Merah they would have had a chance of capturing him alive.

Some Israeli security experts were even more scathing of the operation.

"The French security forces failed in their mission," former special forces officer Lior Lotan wrote in the top-selling Yediot Aharonot daily.

"Either there was a problem in the operational planning or they had to go into action before completing all their preparations," he added.

Former commando officer Uri Bar-Lev wrote in the rival Maariv newspaper: "This is not how a professional unit to combat terror behaves."

And Alec Ron, a former head of the Israel police commando unit, told Israeli public radio the French operation appeared to be characterised by "utter confusion and unprofessionalism".

"It seems to me like an absolute disgrace," he added.

France is home to western Europe's largest Jewish and Muslim communities.

US congressman Peter King said Friday that Merah should have been sent to Guantanamo after Afghan police arrested him in 2010 and handed him over to US troops.

"But the failure to use Guantanamo, as an available safe place to incapacitate terrorists, endangered us and our allies, with tragic results in this case," said King, a Republican congressman from New York.

French police meanwhile prolonged the detention of Merah's mother and brother, whose girlfriend was also still detained, a legal source said.

Police and prosecution officials have said that Merah's brother, Abdelkader Merah, is himself a radical Islamist, and that traces of what could be an explosive material had been found in his car.

President Nicolas Sarkozy, who is seeking re-election in May, was back on the campaign trail Friday, having vowed the day before to crack down on extremism.

Before the Toulouse crisis blew up, he was beginning to close the gap in opinion polls on his Socialist rival Francois Hollande.

In the wake of the bloody end to the siege, Toulouse remained on edge.

Police evacuated the main city square Friday evening when a suspect package was found, and a police demining squad later blew up the object.