A senior Japanese government figure arrived in Algeria Wednesday to meet the prime minister, the foreign ministry said, as Tokyo sought to learn why at least seven of its citizens died when Islamists overran a gas plant.

Senior Vice Foreign Minister Shunichi Suzuki was aboard a government jet that is set to take home the bodies of those known to have been killed in the hostage crisis, as well as seven Japanese nationals who survived.

The fate of three others who were at the desert plant remains unknown, but Japan is bracing for news of their deaths, several days after the Algerian military ended the siege.

Suzuki is carrying a letter addressed to Algerian President Abdelaziz Bouteflika from Japan's Prime Minister Shinzo Abe, Chief Cabinet Secretary Yoshihide Suga told reporters in Tokyo.

"The government will use whatever means possible to confirm what has happened to the three people who are still unaccounted for," he said.

Japan has asked Algeria to fully investigate events at the gas plant and exactly how individuals died, he said.

"Algeria has promised to cooperate as much as possible," Suga said.

Five foreigners are still missing and the bodies of seven other people are so badly charred that they have not yet been identified.

Suga's comments came as it emerged that Japan, Britain the US and other countries whose nationals were caught up in the events at In Amenas issued a joint demarche to Algeria on Friday.

A demarche is a formal diplomatic move in which a country's stance is conveyed in person -- rather than by note -- to another government.

In a conference telephone call, Japan's Vice Foreign Minister Minoru Kiuchi told Algerian foreign minister Mourad Medelci that Tokyo wanted the utmost priority placed on actions that would keep captives alive.

"Japan is strongly concerned about acts that put the lives of the hostages at risk, and it is regrettable that the Algerian Government pressed military rescue operations," he said, according to a foreign ministry statement.

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.

Algeria's government said 37 foreigners of eight different nationalities and an Algerian were killed in the four-day siege, which ended Saturday.

The plane's arrival in Algeria came as Tokyo announced it was shutting its embassy in neighbouring Mali, evacuating staff and urging its nationals in the country to leave because of the deteriorating security situation there.

The Japanese death toll in the Algerian hostage crisis has shaken a country not accustomed to its citizens being made targets abroad.

The kidnappers claimed they launched their attack in the Sahara in protest at Algeria's complicity in a French military campaign against Islamists in Mali.

The French-led offensive in its former colony began early in the New Year, 10 months after the government lost over half its territory to Islamists, amid rising fears that the vast north of the country could become a haven for Al-Qaeda.