Twenty five people were killed in the suicide bombing that targeted a Shia mosque in Kuwait, the Interior Ministry said in a statement carried by state news agency KUNA.
The Ministry also said that 202 people were wounded in the attack, which targeted the packed mosque during Friday prayers.
The Islamic State group claimed responsibility for the attack in a statement posted on social media and said it had targeted a "temple of the rejectionists" — a term it generally uses to refer to Shias, whom it regards as heretics.
It was the first suicide bombing attack on a Shia mosque in the small Gulf Arab oil exporting state, where Sunni and Shia Muslims live side by side with little apparent friction.
Islamic State had urged its followers on Tuesday to step up attacks during the Ramadan fasting month against Christians, Shias and Sunni Muslims fighting with a U.S.-led coalition against the ultra-hardline jihadist group.
Kuwaiti parliament member Khalil al-Salih said worshippers were kneeling in prayer when the bomber walked into the Imam Sadiq Mosque and detonated his explosives, destroying walls and the ceiling.
"It was obvious from the suicide bomber's body that he was young. He walked into the prayer hall during sujood (kneeling in prayer). He looked ...in his 20s, I saw him with my own eyes," he told Reuters by telephone.
"The explosion was really hard. The ceiling and wall got destroyed," he said, adding that more than 2,000 people from the Shia Ja'afari sect were praying at the mosque.
Kuwait City Governor Thabet al-Muhanna said at least 10 people were killed in the attack. Arab satellite channels Al Jazeera al al-Arabiya have put the death toll at 24.
The Health Ministry said Kuwait's blood bank had opened additional centres to receive blood donations and it urged citizens with non-urgent medical needs to avoid the emergency units.
Kuwaiti television showed footage of the emir, Sheikh Sabah al-Ahmed al-Sabah, visiting the damaged mosque in the eastern Kuwait City district of al-Sawabir.
Prime Minister Sheikh Jaber al-Mubarak al-Sabah, who visited the wounded at the Emiri Hospital, condemned the bombing as an attempt to jeopardise Kuwait's national unity.
"This incident targets our internal front, our national unity," Sheikh Jaber told Reuters outside the hospital. "But this is too difficult for them and we are much stronger than that."
The Interior Ministry told citizens to stay away from the scene to allow authorities to investigate.
Islamic State has recently twice targeted Shia mosques in neighbouring Saudi Arabia and carried out attacks against members of the sect's Zaydi branch in Yemen.
Yaqoub Al-Sanea, the Minister of Justice, Religious Endowments and Islamic Affairs, said that despite Friday's attack, "Kuwait will remain an oasis of security for all groups of Kuwaiti society and all sects. The government is taking many procedures to protect prayers and mosques".
