PARIS (AFP/REUTERS) - A "commando" of people arrested or killed in a massive police raid in a Paris apartment on Wednesday (Nov 18) were a terror unit capable of staging a fresh attack, the city prosecutor said.

"A new team of terrorists was neutralised and all indications are that given their arms, their organisational structure and their determination, the commando could have struck," said Paris prosecutor Francois Molins.

The fate of Abdelhamid Abaaoud, the suspected mastermind of the Paris attacks, remained unknown after the massive police assault on his alleged hideout, Mr Molins said, as he outlined a seven-hour raid of "extreme difficulty" which saw police fire nearly 5,000 rounds of ammunition in a battle with a group holed up in two apartments.

A gargantuan probe undertaken since the Friday attacks saw police pore over video footage, telephone surveillance and witness reports which led them to the apartment in the poor multi-ethnic suburb of Saint-Denis.

Mr Molins said a witness report received on Monday led investigators to believe that Abaaoud, a known Belgian militant believed to be in Syria, was in fact on French territory.

"This is an individual suspected of being the instigator of a large number of attacks in Europe," said Molins.

Wary about the report, investigators ran "numerous telephonic and bank verifications", he added.

The police assault was launched at 4.20am, putting Saint-Denis on lockdown as helicopters buzzed in the sky and snipers took up position on rooftops.

However, police immediately ran into difficulty.

"The reinforced door of the apartment at first resisted explosives laid by Raid (anti-terror police) which allowed the terrorists to prepare their riposte," said Mr Molins.

"Very sustained gunfire continued for nearly an hour," he said, adding that "the complex nature of the operation required the use of assault rifles, snipers and explosives."

The operation was further complicated by an explosion - later determined to be a woman who "detonated an explosives vest" - and damage done to the building which led to the collapse of part of the floor.

Another body "riddled with bullets" was found in the debris, but the state of the corpse did not allow for it to be identified.

Therefore, Mr Molins said that "I am not able to give you a precise number and identity of those killed. There are at least two dead and verifications will likely take longer than expected" due to the state of the apartment building.

Three suspects were arrested inside the building, while outside police took into custody a man who lent the apartment to the militants and a woman accompanying him.

Two men were arrested after being found in the rubble.

An eighth man, who was injured and found outside, was also taken into custody believed to have been involved in providing the apartment.

The vast probe also led police to discover a cellphone belonging to one of the attackers in a dustbin outside the Bataclan music venue, scene of the worst violence, where 89 people were gunned down.

A total of 129 people were killed and 350 injured in the attacks.

The phone showed one of the gunmen had sent a message saying "we're ready, let's go".

The message was sent at 9.42pm, before the attack on the Bataclan, Mr Molins said, adding that police were investigating who the message was sent to.

"We can say that a massive logistical operation was meticulously put in place by these terrorists," he said.

Overall, seven men and a woman were arrested at the apartment or nearby.

The Washington Post, citing two intelligence officials, reported on Wednesday that Abaaoud was dead.

The Post did not provide details, including the intelligence officials' nationalities, and Reuters could not immediately confirm the report.