However, Al Jazeera reported that 24 people were killed in the attack on Al-Sadiq mosque, citing medical sources.
A witness told AFP that “dozens were killed and wounded” in the attack. Footage showed several bodies on the floor.
Emergency services rushed to the mosque, which is one of the largest Shiite worship centers in Kuwait.
A statement by Islamic State identified the bomber as Abu Suleiman al-Muwahed, and called the mosque a “temple of the rejectionists” – a term used by the group to refer to Shiite Muslims.
Kuwait’s prime minister said the suicide bombing was an attempt to threaten Kuwait’s national security.
The attack is the first such bombing targeting Kuwaiti Shiites, who make up around one-third of the country’s native population of 1.3 million people.
Friday midday prayers are typically the most crowded of the week, and attendance increases during the holy Muslim month of Ramadan, which started last week.