PARIS, March 24 (Xinhua) -- French President Emmanuel Macron on Saturday announced a national tribute to a gendarme who succumbed to his injuries after he voluntarily swapped himself for a female hostage during an attack on a supermarket in Trebes, southern France, on Friday.

Macron "decided that a national tribute would be organized in honor of Lieutenant-Colonel Arnaud Beltrame who sacrificed his life to protect our fellow citizens," his office said without giving further details.

Beltrame, 44 , offered himself up unarmed to the attacker in exchange for the woman who was taken as a human shield, and managed to leave his phone on a table with an open line so that police could hear what was going on inside the supermarket.

Once gunshots were heard, police launched the assault and killed the gunman.

The gendarme, who once served in Iraq, was seriously injured in Friday's attack and succumbed to his injuries in hospital where he was rushed once the siege ended.

The gunman, identified as 25-year-old Redouane Lakdim, began his rampage by hijacking a car on Friday morning in the southern French town of Carcassone. He shot one passenger dead and injured the driver. The body of the victim was later found hidden in a bush.

Lakdim then opened fire on police officers jogging in Carcassone, injuring one person. Following that, he drove a few kilometers to Trebes and headed into a Super-U supermarket around 10 a.m. local time (0900 GMT).

He stormed the supermarket, shouting "Allahu Akbar" --God is great -- and telling the 50-odd people inside that he was "a soldier of the Islamic State" seeking "to liberate brothers."

Lakdim killed four people and injured 15 others.

While the Islamic State (IS) claimed responsibility of the attack, several hundred investigators were still checking the claim and looking into possible complicity the attacker could have benefited from to carry out his attacks and how he had been radicalized, the Elysee said after Macron met with concerned ministers and army chiefs.

A 18-year-old woman and a minor believed to be Lakdim's friend were put into police custody for criminal association.

According to local media, three improvised explosive devices, a 7.65-millimetre handgun and a hunting knife were found in the supermarket.

Reports added searches at the attacker's home showed notes referring to the IS that appeared to be a testament, as well as a phone and a computer.