Updated 6.30pm

The Islamic State group has claimed an attack on a Bangladesh restaurant in which militants killed 20 hostages, saying it targeted the citizens of "Crusader countries" in the capital, Dhaka.

The statement was circulated by supporters of the group on the Telegram messaging service Saturday. It resembled previous statements released by the extremist group.

Nine of the dead hostages were Italian, seven were Japanese and one was Indian, according to those countries.

It was not immediately clear if the Islamic State leadership in Syria and Iraq was involved in the planning the attack. IS has previously claimed attacks carried out by so-called lone wolf attackers with no known connection to the group.

Bangladesh Army Brigadier General Naim Asraf Chowdhury speaks during a news conference.

Japan's chief cabinet secretary Yoshihide Suga said on Saturday night in Tokyo that five men and two women who were Japanese had died in the attack.

They were among eight Japanese nationals eating at the restaurant. One man who had been shot was rescued, and being treated at a hospital.

The Japanese were consultants working on a Japanese government aid project in Dhaka.

The bodies of nine Italians were identified, the Italian foreign minister said.

Paolo Gentiloni told reporters that there was another, unidentified body in the military morgue of Bangladesh but the nationality has not yet been determined.

Italian news reports had said around 10 Italians were inside the restaurant in Dhaka when it was attacked by militants.

One of the victims of the attack had earlier been identified by Italian media as a 47-year-old manager from north-eastern Italy.

Italian agency Ansa said the man, who was married and the father of three-year-old twin girls, was in Bangladesh for work.

Ansa said word spread in the town of Feletto Umberto, near Udine, on Saturday that the man was among the 20 who died in the attack by extremists.

The White House said a US citizen was among the hostages killed.