An undated and non-datelined frame grab from a video broadcast by French national television station France 2 who they claim to show Mohamed Merah.

Questions mounted over how a known Islamic extremist managed to murder seven people, including three children, in three separate attacks before being killed in a firefight.

Adding to pressure on security officials one veteran police officer asked how the gunman was not taken alive during the siege and final assault in the southwestern city of Toulouse, in which the gunman died on Thursday.

Officers from an elite unit moved in on Thursday morning after a 32-hour siege, killing self-proclaimed al-Qaeda militant Mohamed Merah as he tried to shoot his way out of his apartment.

The siege had interrupted the hard-fought campaign for France's April-May presidential vote, but Sarkozy resumed his re-election bid with a rally in the city of Strasbourg on Thursday evening.

“These crimes were not the work of a madman,” he said.

“A madman is irresponsible. These crimes were the work of a fanatic and a monster.”

In a televised address earlier, Sarkozy vowed to crack down on extremism, saying he wanted legal action against people who regularly consulted jihadist websites or travelled abroad for indoctrination.

But some politicians were already asking how French intelligence officers had failed to head off Merah's killing spree, given that he was already on their radar as an extremist.

Sarkozy's main challenger Francois Hollande referred to reports of possible failings in the surveillance of Merah at a rally late Thursday.

With the end of the siege, he said, “questions will have to put.”

Earlier on Thursday, French Foreign Minister Alain Juppe said in an interview with Europe 1 radio that French intelligence officers had recently questioned Merah.

While he did not know if the intelligence service was at fault, he acknowledged the matter would have to be investigated.

Already Wednesday Marine Lepen, the presidential candidate for the far-right National Front had accused authorities of having underestimated the rise of Islamic fundamentalism in France.

An al-Qaeda linked group, Jund al-Khilafah, claimed responsibility on jihadist websites for the killings.

During the siege, Merah told police he had carried out all three recent attacks. In the first two, last week, he shot dead three soldiers. Then on Monday he gunned down three children and a teacher at a Jewish school.

France's chief anti-terror prosecutor Francois Molins confirmed that Merah had filmed the attacks with a video camera.

The killings shocked France, home to western Europe's largest Jewish and Muslim minorities.

On Thursday morning the streets of a residential area in Toulouse were filled with the sound of intense gunfire in a shattering finale to the standoff, which had begun before dawn the previous day.

As police from the elite RAID force stormed his apartment the 23-year-old burst out of the bathroom wearing a black djellaba, a traditional loose-fitting North African robe, and a bullet-proof vest.

He opened fire on them before jumping out the window of his first-floor apartment, still firing as he fell. Molins said Merah was shot in the head.

“He was dead by the time he hit the ground,” one police source told AFP.

Police had been told to do everything possible to take Merah alive, but had had no choice but to fire, said Molins.

“He literally launched an assault, rushing forward with a Colt .45 and continuing to fire as he jumped through the window, until he was shot in the head,” he told journalists.

And RAID head Amaury de Hauteclocque said: “It's the first time in my life I've seen someone, as we launch an assault, launch an assault against us.”

But Christian Prouteau, who founded the GIGN - another of France's elite police units - wanted to know why police had not used tear gas to flush out Merah, expressing astonishment that they had failed to capture him alive.

In an interview, with Ouest France newspaper, he asked: “How come the police's best unit did not manage to arrest a man all alone?”

During the two-day operation at Merah's apartment, five officers were wounded, but none of their injuries was life threatening, said Molins.

Merah had said his attacks were to avenge Palestinian deaths and to punish France for its military presence in Afghanistan and the ban on full-face veils, Molins said.

He claimed to have been trained by al-Qaeda in Waziristan, a tribal area of Pakistan known as a haven for Islamist insurgents connected to Taliban guerrillas.

He had twice travelled to the region, said Molins, on one occasion being arrested by Afghan police and handed over to US army troops. They put him on a flight back to France.

A US intelligence official told AFP that Merah had been on America's “no-fly” list and was banned from boarding flights to or from the country.

The al-Qaeda linked Jund al-Khilafah, claiming responsibility on jihadist websites for the killings, said “the Frenchman carried out an operation that shook the foundations of the Zionist Crusaders.

“Israel's “crimes... will not go unpunished,” the statement added.

According to US monitoring group SITE, Jund al-Khilafah has previously claimed attacks in Afghanistan and Kazakhstan.

Merah had filmed the killings with a camera attached to a chest harness, Molins confirmed Thursday. Officers had viewed the footage.

During the March 11 shooting of a paratrooper in Toulouse, he can be heard saying “You kill my brothers, now I'm killing you”, Molins said.

In the March 15 attack, when he killed two other paratroopers in nearby Montauban, he can be seen gunning down the soldiers before driving off on a scooter shouting “Allahu Akbar!” (God is Greatest!).

On Monday the gunman, again wearing a motorcycle helmet and riding a scooter, attacked the Ozar Hatorah Jewish school in Toulouse, killing a religious studies teacher, his two young sons and a seven-year-old girl. - Sapa-AFP