Japan's government Thursday confirmed a tenth victim of the Algerian hostage crisis, the highest death toll of any nation, as friends and colleagues of those who perished paid tribute at a makeshift altar.

The announcement came as the seven Japanese men who survived after Islamist gunmen laid siege to the desert gas plant headed home aboard a government plane that was also carrying the bodies of nine victims.

"We have now identified the final body," Chief Cabinet Secretary Yoshihide Suga told reporters. "We have confirmed the death of a total ten people."

"The government for its part wishes to express its heartfelt condolences to the bereaved families," said Suga.

Japan's body count of 10 is the highest of any nation whose citizens were caught up in the crisis in the Sahara and an unusual taste of Jihadist anger for a country that has remained far from US-led wars in the Muslim world.

At the headquarters of plant-builder JGC, which employed -- directly or indirectly -- all Japanese at the complex, mourners dressed in black solemnly bowed to a Buddhist cenotaph, urging departed souls to find peace.

An elegantly handwritten prayer for those who lost their lives was inscribed on the wooden tablet, around which lay bouquets of white flowers.

The loss of so many colleagues is a heavy blow to JGC in a country where corporate communities are close-knit and company loyalties remain strong.

Media reported Thursday that the tenth Japanese victim of the Islamist gunmen's rampage was Tadanori Aratani, 66, a former vice president of JGC and lately its supreme adviser.

The government has so far refused to identify those who died, although newspapers and broadcasters have told the stories of some victims, including heart-wrenching tales of never-to-be-realised plans for family celebrations.

Broadcaster NHK spoke to the sobbing elderly mother of one man struggling to come to terms with the loss of her son less than two years after the March 2011 tsunami swept her husband to his death.

The plane carrying survivors and bodies left Algeria on Thursday, bound for Tokyo's Haneda airport.

Kyodo reported that post-mortem examinations will be carried out in Japan to determine exactly how each person died.

A country badly shocked by the horrors of the last week awaits the seven Japanese survivors of the siege, some of whom had the grisly task of identifying dead colleagues before they left Algeria.

Japan was among the more forthright of nations as the hostage crisis unfolded, summoning the Algerian ambassador to demand answers on the situation and press for restraint from the army.

World capitals have since rowed back from comments that may have been seen as overly critical in Algiers, and have repeatedly stressed that the hostage takers bear full responsibility for the desert outrage.