Dhaka: Islamic State militants slaughtered at least 20 civilians, most of them foreigners, with sharp weapons before security forces on Saturday morning rescued 13 hostages and gunned down six gunmen, ending a long drawn-out overnight siege at a Bangladesh cafe popular with both locals as well as foreign visitors, officials said. "Most of the victims were killed brutally with sharp weapons," Brigadier General Nayeem Ashfaq Chowdhury, director of military operations, told reporters here, after the deadly standoff between government forces and suspected Islamic State militants ended. Officials were still trying to ascertain the nationalities of those killed. He said security forces after the "Operation Thunderbolt" recovered bodies of 20 victims lying on the blood splattered floor of the restaurant along with unexploded IEDs, sharp weapons and a communication device. Tuhin Mohammad Masud, a commander of the elite Rapid Action Battalion, said one of the gunmen, who was injured in the shootout, has been arrested. "We have gunned down at least six terrorists." The attack, which also left two policemen dead, began Friday evening after heavily armed gunmen stormed the Holey Artisan Bakery, a popular hangout for foreigners, in the high-security and affluent Gulshan diplomatic zone of the Bangladesh capital. The neighbourhood was considered safe with high walls security guard booths and gated driveways at many entry points of the enclave. Prime Minister Sheikh Hasina condemned the "extremely heinous act" and said 13 hostages were rescued. "What kind of Muslims are these people? They don`t have any religion," Hasina said in a televised address to the nation. "People must resist these terrorists. My government is determined to root out terrorism and militancy from Bangladesh." Officials said that the 13 rescued hostages included many foreigners, including a Japanese and two Sri Lankans. At least eight Japanese citizens were among the hostages. Earlier, army men and navy commandos stormed the café to bring an end to the deadly siege in the morning after night-long intermittent exchange of fire and explosions. Armoured vehicles moved in the Gulshan neighbourhood. At least two police officers were killed in earlier exchanges of fire and 30 police officers were injured. 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. Witnesses narrated chaos as the gunmen shouted 'Allahu Akbar' (God is great) when they stormed into the café and began firing blanks. Cafe worker Sumon Reza said he escaped as the gunmen came in. The Daily Star reported that hostages were made to recite verses from the Quran and those who could were not harmed. "The others were tortured by the gunmen," said Rezaul Karim, father of one of the hostages Hasnat Karim, told the daily. Karim had gone to celebrate his 13-year-old daughter's birthday along with his wife and son Rayan, 8. The family was rescued early in the morning. This is for the first time that militants in Bangladesh have held foreigners hostage. But the deaths in the attack are the latest in a series of dozens of deadly attacks by Islamic State and Al Qaeda-linked militants targeting progressive academics, writers, activists and religious minorities in the majority Muslim country. The attack came just hours after a Hindu priest was killed in Bangladesh on Friday. The attack drew calls for Bangladesh government to act against terrorism firmly. Neighbouring India called for quick action to adopt the long-stalled Comprehensive Convention on International Terrorism (CCIT) and expressed disappointment that the UN General Assembly failed to push for its early adoption. "The perpetrators of terrorist attacks as well as the states that support and sponsor or provide safe havens to terrorists or terrorist groups must be made accountable," India's Permanent Representative Syed Akbaruddin said, speaking at the General Assembly.