A man wearing a Muslim tunic has been arrested on suspicion of slitting the throats of his father and brother in a Paris street this morning, it has emerged.

The alleged attacker shouted Allahu Akbar as he knifed the two men in Rue de Montreuil in the east of the French capital this morning, according to a police source.

Horrified witnesses saw one victim lying in a pool of blood outside a building.

A man wearing a Muslim tunic has been arrested on suspicion of slitting the throats of his father and brother in a Paris street this morning, it has emerged. Police are pictured at the scene in Rue de Montreuil, eastern Paris, this morning

The alleged attacker shouted Allah Akbar as he knifed the two men in Rue de Montreuil (pictured today) in the east of the French capital this morning, according to a police source

The circumstances of the attack were unclear but some witnesses said the suspect made remarks 'linked to radical Islam'.

Police urged caution, saying the killer's motives were unknown.

A resident of the high-rise building in the city's 11th district said he heard a man 'crying for help' at around 10am.

'I looked out the window and saw a man lying on the ground. There was a lot of blood.

'There was another man standing beside him, dressed in a white djellaba (loose-fitting tunic worn by some Muslims).

'He fell to his knees and prayed until the police came to take him away,' 21-year-old Thomas told AFP.

The circumstances of the attack were unclear but some witnesses said the suspect made remarks 'linked to radical Islam'

Investigation: Horrified witnesses saw one victim lying in a pool of blood outside a building

Another resident, 64-year-old Francois Petitjean, described a harrowing scene.

'When I arrived in the hall of the building I saw a body lying in a pool of blood, in front of the postboxes.

'It was carnage. I went out and then saw another person covered in blood,' he said, expressing shock.

Police had sealed off a section of the street around the building. No further details on the suspect or the victims were immediately available.

It comes as France remains on high alert after a wave of Islamist terror attacks over the last two years.

In 2015, ISIS fanatics went on the rampage in the French capital slaughtering 130 in a wave of machine gun and suicide bomb attacks.