The father of the gunman who embarked on a deadly shooting spree at a Christmas market in Strasbourg has said his son was an Isis supporter, as officials said a fifth person had died from their wounds.

Abdelkrim Chekatt said Chérif Chekatt, 29, believed the Islamic terror group was “fighting for a just cause”.

Five people were killed and 12 others were wounded in the gun attack on Tuesday.

The Paris prosecutor's office said a Polish national became the fifth victim on Sunday.

Chekatt escaped but was cornered by French police and shot dead in the Neudorf area of the city following a huge two-day manhunt.

His parents and two brothers were among seven arrested as police investigated whether others were involved in the attack.

The four family members have since been released “due to the lack of incriminating evidence at this stage”, the Paris prosecutor’s office said.

Speaking to the TV channel France 2, Abdelkrim Chekatt denied knowing his son was planning the shooting and said he had tried to discourage his extremist beliefs.

“He’d say, for example, that Daesh is fighting for a just cause,” he said, using the Arabic acronym for Isis. “I told him: ‘Forget about Daesh, don’t listen to what they say. Don’t you see the atrocities they commit? Beheadings, burning people alive.’”

Mr Chekatt, who said he last saw his son three days before the shootings, added: “I always told him, ‘Daesh, they are criminals.’”

Isis’s propaganda wing has described Cherif Chekatt as a “soldier”, but French authorities say there is no evidence the group was involved in the attack.

The country’s interior minister, Christophe Castaner, said Isis’s claim of responsibility was “totally opportunistic”.

Chérif Chekatt was shot dead by police following a two-day manhunt (AP)

But Cherif Chekatt was on French security services’ watch list for radicalism and had 27 criminal convictions for offences in France, Germany and Switzerland.

Investigators are trying to determine whether he had accomplices in the Christmas market attack.

The three other people arrested, who are not family members but were close to Chekatt, remain in custody.

His father said he went to police of his own accord on the night of the shooting spree.

He claimed he had offered to “reason with” his son to convince him to give himself up if police found him.

If he had known his son was planning a deadly rampage, he would have “denounced him, and he wouldn’t have killed or been killed”, Mr Chekatt added.

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A memorial for the shooting victims was held in Strasbourg’s Kleber square on Sunday.

The service took place close to the eastern city’s popular Christmas market, which is the largest in France.