Twenty people, all of them foreigners, were killed during an attack by suspected Islamist militants on a cafe in Bangladesh, the army says.

Gunmen stormed the Holey Artisan Bakery cafe in Dhaka late on Friday before troops entered almost 12 hours later.

Six of the attackers were also killed and one was arrested, a government spokesman said. The attack was claimed by the so-called Islamic State (IS).

Italy's Prime Minister Matteo Renzi confirmed Italians were killed.

He offered condolences to the victims' families and, referring to the attackers, said: "Our values are stronger than hatred and terror."

Italian news agency Ansa said up to 10 Italians may be unaccounted for. The Italian press said many of those dining at the cafe worked in the garment industry.

In other developments:

- India's foreign minister said one Indian national was among the dead

- Bangladesh Army Brig Gen Naim Asraf Chowdhury said the victims had been "brutally" attacked with sharp weapons

- Japan's Deputy Chief Cabinet Secretary Koichi Hagiuda said seven other Japanese nationals were in the cafe, but that the government had not yet been able to contact them

- Gen Chowdhury said 13 people were rescued, including one Japanese national and two Sri Lankans

The siege began as diners were gathering to break their fast during the Muslim holy month of Ramadan.

"It was an extremely heinous act," Prime Minister Sheikh Hasina said in a televised statement. "What kind of Muslims are these people? They don't have any religion.

"My government is determined to root out terrorism and militancy from Bangladesh."

Bangladesh's Daily Star newspaper said the gunmen tortured anyone who was unable to recite the Koran. They provided meals overnight for only the Bangladeshi captives, it said.

Sumon Reza, a supervisor at the cafe, was in the restaurant in Gulshan district when the attack began, but managed to flee to the roof.

"The whole building was shaking when they set off explosives," he told media in Bangladesh. He later jumped off the roof and escaped.

"From 08:00 it all started," said Rashila Rahim, who lives near the cafe. "Gunshots, tank sounds... It was like we were in the middle, and gunshots from all around."

The attack began when eight or nine armed men burst into the cafe in the diplomatic area of the city at about 21:20 (15:20 GMT) on Friday and opened fire.

Media reports quoted witnesses as saying that "Allahu Akbar", meaning "God is great", was heard as the militants entered the cafe, which is popular with expatriates, diplomats and middle-class families.

At least two police officers were killed in exchanges of fire late on Friday, and 30 police officers were injured.

A statement on the IS's self-styled Amaq news agency said militants had attacked a restaurant "frequented by foreigners". It said that more than 20 people "of different nationalities" had been killed but this has not been confirmed.

Lt Col Tuhin Mohammad Masud, commander of the Rapid Action Battalion, told Associated Press the gunmen did not respond when asked to negotiate. It is unclear if they made any demands.

The attack comes after a spate of murders of secular bloggers, gay activists, academics and members of religious minorities, blamed on Islamist militants.