Kuwait's interior minister has said the country at war in the wake of an Islamic State (formerly known as Isis) bombing on a Shia mosque which left 27 worshippers dead.

The attack on 26 June, which coincided with Islamic State inspired attacks in Tunisia and France, was the worst of its kind in the Arab kingdom.

One bomber, identified by IS as Saudi Fahd Suliman Abdul-Muhsen al-Qabaa, entered the Imam Sadiq mosque and blew himself in a packed crowd up during Friday prayers at the end of the second week of Ramadan.

Kuwait's interior ministry has now confirmed that the attack was planned for maximum effect and that the cell which carried out the bombing had considered two other targets in its preparation.

"We are in a state of war. It's a war that had been decided with this cell. But there are other cells, and we will not wait for them to try their luck with us," Interior Minister Sheikh Mohammad Al-Khaled Al-Sabah told parliament.

Reuters reported that a total of 60 individuals have been detained in connection with the mosque attack and that a charity collecting money for Syria has been closed for because of its links to Islamic militants.

A Kuwaiti local paper has reported that several suspects had confessed to receiving payments from abroad to carry out the attacks.

Kuwait has stepped up security after the bomber, Fahd Suliman Abdul-Muhsen al-Qabaa, flew in from Saudi Arabia hours before detonating himself.

In a posthumous audio message stamped with Islamic State's logo and posted online, al-Qabaa called Shia Muslims "enemies of God everywhere, especially in Kuwait."