BRUSSELS (AFP) - The arrest of Europe's most wanted man Salah Abdeslam may be a "major blow" to militant networks but the four-month manhunt also highlights serious failures which need to be fixed, commentators and officials said Saturday.

"From Molenbeek to Molenbeek," ran the headline in Le Soir, neatly summing up Abdeslam's trajectory from the gritty Brussels neighbourhood he called home to the Nov 13 attacks in Paris which claimed 130 lives, and then back again, to his dramatic capture Friday.

"This spectacular arrest allows Belgium to dust off its pride," editor in chief Beatrice Delvaux wrote in Le Soir daily.

"It has to be said that Belgium's reputation was at rock bottom with Abdeslam on the run, not only a security threat but also a direct challenge to the authorities," Delvaux said.

For other commentators, however, the fact it took four months to track Abdeslam down to Molenbeek, just 500m from the family home showed the authorities were not up to the job.

"This long escapade is not a great success for the Belgian intelligence services," French lawmaker Alain Marsaud said.

"Either Salah Abdeslam is very clever, or the Belgian authorities services are stupid, which is more likely," said Marsaud, a member of an ongoing French parliamentary inquiry into possible security failings over the November attacks.

Belgian Federal Prosecutor Frederic van Leeuw hit back Saturday, saying "the dossier was a huge puzzle which had to be put together patiently piece by piece."

He told Belgian television station RTBF the investigation was also made more "complicated by outside pressure, at the French political level, which of course I understand because there were so many victims."

Abdeslam fled Paris immediately after the attacks, slipping back to Brussels where investigators now believe he remained, rather than disappearing overseas as many had initially thought.

In December, they found his fingerprints in another Brussels apartment and searches turned up tantalising evidence that their quarry might not be so far away.

Then on Tuesday, they picked up the trail again during a raid on a house in the Forest area of the capital where investigators found his fingerprints.

Police shot dead one man in that raid but two others escaped despite a huge security operation amid speculation - denied - that one of them might have been Abdeslam.

The authorities said initially they were simply carrying out a routine search in Forest and were not expecting to come across any militants.

But chief prosecutor Van Leeuw said Saturday that "they were not in Forest by accident. It's not just any team that was there, it was the police anti-terrorist unit."

Then the authorities got a lucky break when they intercepted a "desperate" phone call by Abdeslam to relatives in Molenbeek seeking refuge, police sources said.

Another source close to the investigation said police were also tipped off by someone who told them they had been contacted by a man claiming to be Abdeslam looking for help.

"There are questions because he kept to a rather small area in Brussels," said Louis Caprioli, former head of the French anti-terrorist Directorate of Territorial Surveillance (DST).

"It raises questions about how the Belgian police monitored movements in the area. Was it enough? Did they have enough informants and contacts? I'm not sure," Caprioli said.

He added: "To be on the run for four months, he clearly benefitted from several support networks."

Abdeslam had "friends in the criminal world, among Islamic radicals, then there's his childhood friends in the neighbourhood," said Caprioli.

"It's a big job. Perhaps Belgian law enforcement might be a bit off the pace but at the same time they had to deal with a large population (in Molenbeek), part of which is radicalised. It's not easy to get access."

Prosecutor Van Leeuw noted that nearly 100,000 people live in Molenbeek "and then you have 10 individuals who are able to do these things."

"Locking down an entire neighbourhood to search every home with a fine-tooth comb, I think, is just not consistent with democracy and our values," he said.