At least four people have been killed in a suicide bomb attack on a Shia mosque in the Kuwaiti capital.
Many people were injured, and unconfirmed reports put the death toll much higher.
The blast hit during Friday prayers at the Imam Sadiq Mosque in al-Sawaber, a busy area to the east of Kuwait City.
An Islamic State- (IS) affiliated group said it was behind the attack. IS has carried out similar recent attacks in neighbouring Saudi Arabia and Yemen.
The governor of Kuwait City, Thabet al-Muhanna, told Reuters four people had died in the suicide attack. However, the AFP news agency said at least 13 people were killed. At least eight people were reportedly wounded.
A Kuwaiti MP, who saw the attack, said the mosque was packed with some 2,000 people when there was a loud explosion, Reuters news agency reported.
Footage posted online said to be from the scene of the attack showed men, some in blood-splattered clothing, walking around a smoke-filled room with rubble on the floor.
Al-Jazeera also reported that the Kuwaiti emir was heading to the scene of the blast.
Sunni-ruled Kuwait has a large Shia minority, which IS considers to be heretics.