DHAKA: All the attackers in the assault on a cafe in Dhaka in which Islamic State terrorists slaughtered 20 civilians, mostly foreigners, including an Indian, were Bangladeshi citizens and five of them were wanted by police.

Police Inspector General Shahidul Hoque told CNN that police had tried to arrest these five militants previously.

Authorities also released the nationalities of the 20 hostages who were found dead inside the Holey Artisan Bakery cafe after Bangladeshi troops stormed the cafe early Saturday morning, ending an overnight siege.

According to the country's Joint Force Command, nine of the victims were Italian, seven were Japanese, one was from India, two were Bangladeshi and one was a US citizen of Bangladeshi origin. Eleven of the victims were male and nine were female.

Two police officers were also killed in a gunfire exchange earlier in the standoff, authorities said.

Security forces rescued 13 hostages and killed six gunmen on Saturday morning, ending the nation's worst hostage crisis, being termed as Bangladesh's '7/16'.

Bangladesh Prime Minister Sheikh Hasina has called a two-day state mourning for the victims, who included nine Italians, seven Japanese, three Bangladeshis and an Indian teenager, at the Holey Artisan café in the diplomatic area of Gulshan in Dhaka.

One of the gunmen, injured in the shootout, was captured, while 13 hostages were rescued at the end of the 12-hour siege. The Islamic State has claimed responsibility for the attack.

Indian President Pranab Mukherjee, Prime Minister Narendra Modi and West Bengal Chief Minister Mamata Banerjee have condemned the attack.

Modi called up Sheikh Hasina and condemned the "despicable attack" and said that India "stands firmly with our sisters and brothers of Bangladesh" in this hour of grief.

Indian External Affairs Minister Sushma Swaraj confirmed the killing of 19-year-old Tarishi Jain of Firozabad in Uttar Pradesh.

"Tarishi was 19 years old. She passed out from American School Dhaka. Presently, she was a student at Berkeley," Sushma posted.

In Dhaka, Brigadier General Nayeem Ashfaq Chowdhury, director of military operations, told reporters that "most of the victims were killed brutally with sharp weapons".

The attack began at 8.45 p.m. when around 20-22 guests were at the Holey Artisan Bakery downstairs and the O'Kitchen Restaurant upstairs, a cafe popular with foreigners.

The gunmen, shouting "Allahu Akbar" raided the cafe and took hostages, and slaughtered those who were unable to recite the Quran, said rescued hostages.

Later, the area was sealed off, and following directives from Prime Minister Hasina, the armed forces along with the Rapid Action Battalion and police launched an assault, codenamed 'Operation Thunderbolt', in the morning. The siege ended at 8.30 a.m.

Prime Minister Hasina, condemning the "extremely heinous act", vowed to root out terrorism from the country, which has seen a spate of deadly attacks by Islamic State and Al Qaeda-linked militants on progressive academics, writers, activists and religious minorities in the Muslim majority country.

"We'll establish Bangladesh as a peaceful state…No conspiracy can hinder our advancement," she said in a nationally televised address.

"What kind of Muslims are these people? They don`t have any religion. People must resist these terrorists. My government is determined to root out terrorism and militancy from Bangladesh," she said.

Officials said the 13 rescued hostages included a Japanese and two Sri Lankans.

The Bangladeshi branch of the Islamic State claimed the attack through its mouthpiece, the Amaq news agency, saying 24 people "of different nationalities" were killed and 40 others were injured.

The Daily Star reported that hostages were made to recite verses from the Quran and those who could were not harmed.

The attack has also been condemned by other countries, including Pakistan and Malaysia, while the European Union has also voiced condemnation.