Forensic officers scour the scene for clues - AP

A suspected terrorist on day release from prison executed two female police officers with their own guns and shot dead a trainee teacher before he was killed in a shootout after taking two women hostage at a school in the centre of the Belgian city of Liege.

The bloody rampage on Tuesday morning, which left another four officers wounded, was captured on videos on social media, which showed the black clad man waving a pistol in each hand and shouting “Allahu Akbar” before he was gunned down by elite officers. Belgium's federal prosecutors office has opened an terror investigation into the attack.

The “lone wolf” attacker, 36, was named locally as Benjamin Herman, who was well-known to police for a string of crimes including robbery, assault and drug-dealing and was from Rochefort, a city about an hour from Liege.

One officer was named in local media reports as Soraya Belkacemi, 45, a widowed mother of twins, who are now orphaned. The other was Lucile Garcia, 53, who was described by fellow officers as a "fantastic colleague" who had married her partner a month ago.

Herman was granted temporary release from prison on Monday night until Tuesday, despite a prison service assessment that judged him “ultra-violent” and that he was on a terror watchlist over suspicions he had become radicalised in 2017.

Such “family leave” is meant to help prisoners prepare for their eventual release, which would have been in 2020 in Herman’s case after he had served the sentence he began in 2013. He had been released for two days on 13 previous occasions.

Belgium's federal prosecutors office has opened an terror investigation into the murders, which come after the country was accused of being a hotbed of extremism after the 2015 Paris attacks, which killed 130 people. and suicide bombings in Brussels in 2016 in which 32 died.

The country’s intelligence services came under intense scrutiny for apparently missing a series of leads after the Paris attacks that could have led to the Brussels bombers.

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“He has been reported or presumed to be belonging to the entourage of an Islamist recruiter," a source close to the investigation told AFP. Police have found a koran and prayer mat in the convert’s cell.

Confirming that the attacker was on the police watchlist, lawmaker George Dallemagne, who sits on several Belgian parliamentary security committees, tweeted: "The supervision of radicalised prisoners remains tragically flawed."

Forensic officers scour the scene for clues Credit: Geert Vanden Wijngaert /AP

"It is clear that the assassin's objective was to attack the police," said Christian Beaupere, the head of the Liege police force.

The Liege prosecutor's office said the gunman had "hunted down" the two police officers, who were checking parking meters, before attacking them from behind with a box cutter on a boulevard in the heart of Belgium’s third city at about 10.30am local time.

After stabbing the officers, aged 45 and 53, multiple times, Herman took the officers' guns and shot them dead before opening fire on his next victim, who was sitting in his car. He was named by local press as Cyril Vangriecken, a 22-year-old trainee teacher from Vottem, a nearby town.

Armed Belgian police walk past the scene of the shooting in the centre of Liege Credit: Geert Vanden Wijngaert/AP

Herman entered a nearby high school about 100 yards away and took two female employees, one a cleaning lady, hostage, which forced armed police to swing into action.

Pupils were evacuated to safety and people in the street raced for cover in the ensuing gunbattle when Herman came out firing at police.

Four officers were wounded, two in the legs and two in the arms, before Herman was finally “neutralised” about 30 minutes after he launched his initial attack.

The cleaner was reported to be “safe and healthy”. A major security cordon was set up around the area, while panicked parents came to collect their unhurt children from the school complex.

The national crisis centre said it had not raised its alert level - an indication the man was acting alone and so follow-up attacks were not expected.

Emergency services arrive in Liege's central boulevard on Tuesday morning Credit: VICTORJ_FR/Twitter

Herman was "already on the run" after committing another murder on Monday night in the town of On, in southern Belgium, a source told AFP, though local prosecutors said they have not yet established a link with the Liege incident.

The body of a man shot in the head was found after a jewellery robbery in Rochefort earlier that evening.

Charles Michel, the prime minister of Belgium, condemned the "blind and cowardly violence" in Liege and offered his support for the victims and their families. He called for restraint after images on social media appeared to show the two officers lying metres apart in pools of blood outside a cafe.

Theresa May, the prime minister of Britain, said: "My thoughts are with the victims of today’s cowardly attack in Belgium and their grieving families. The UK stands resolute with our Belgian allies against terror."

Coups de feu à Liège, évacuation du boulevard d’Avroy. Beaucoup de voitures de police sur place + secours #Avroy#Liege#gunshotpic.twitter.com/CLXo16nST3 — Victor ⌬ (@VICTORJ_FR) May 29, 2018

Mr Michel and Philippe, the King of the Belgians, have visited the city. A minute's silence will be held tomorrow and flags flown at half-mast at Liege's town hall, where a book of condolences has been opened.

Liege, an industrial city close to the German border in the French-speaking Wallonia region, was also the scene of a shooting in 2011, when a gunman killed four people and wounded over 100 before turning the gun on himself.

Liege shooting