Armed police stand outside a supermarket in Auckland, New Zealand, Sept 4, 2021. (BRETT PHIBBS/AP)

WELLINGTON - New Zealand Prime Minister Jacinda Ardern vowed on Saturday to tighten counter-terrorism laws this month after a knife-wielding militant known to the authorities stabbed and wounded seven people in a supermarket.

Police shot dead the 32-year-old attacker, a Sri Lankan national who had been convicted and imprisoned for about three years before being released in July, moments after he launched his stabbing spree on Friday.

Ardern said earlier the man was inspired by the Islamic State militant group and was being monitored constantly but could not be kept in prison by law any longer.

The Counter Terror Legislation Bill criminalizes planning and preparation that might lead to terror attack, closing what critics have said has been a loophole allowing plotters to stay free

"I am committing, that as soon as Parliament resumes, we will complete that work – that means working to pass the law as soon as possible, and no later than by the end of this month," Ardern told a news conference.

The Counter Terror Legislation Bill criminalizes planning and preparation that might lead to terror attack, closing what critics have said has been a loophole allowing plotters to stay free.

But Ardern said it would not be fair to assume that the tighter law would have made a difference in this case.

"This was a highly motivated individual who used a supermarket visit as a shield for an attack. That is an incredibly tough set of circumstances," she said.

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Ardern said the attacker came to the attention of the police in 2016 because of his support for a violent ideology inspired by Islamic State.

Police were following the man when he went into the Countdown supermarket in New Lynn mall in Auckland. They said they had thought he had gone in to do some shopping but he picked up a knife from a display and started stabbing people.

Police said they shot him within a minute of the start of the attack.

Ardern said the man arrived in New Zealand in 2011 on a student visa and was not known to have held any extreme views.

He came to the attention of police in 2016 after he expressed sympathy on Facebook for militant attacks, violent war-related videos and comments advocating violent extremism.

In May 2017, he was arrested at Auckland's airport where authorities believed he was travelling to Syria. He was charged after restricted publications and a hunting knife were discovered at his house but was released on bail.

In August 2018, he again bought a knife and was arrested and jailed. He was released into the community in July this year when surveillance began, Ardern said.

Ardern said she wanted to explain why the attacker had not been deported but could not because to do so would violate court suppression orders, which also prevented her from identifying, him, she said.

READ MORE: NZ begins inquiry into Christchurch's mosques massacre

Supermarket group Countdown said on Saturday it has removed knives and scissors from its shelves, a day after the attack in one of the company's stores that left six people injured.

"Last night, we made the decision to temporarily remove all knives and scissors from our shelves while we consider whether we should continue to sell them," said Kiri Hannifin, Countdown’s general manager for safety.

"We want all of our team to feel safe when they come to work, especially considering the events of yesterday," she said in a media statement.

Other supermarket chains had also removed sharp knives from sale, local media reported.