DUBAI: Three brothers have been arrested by Saudi and Kuwaiti authorities for involvement in a suicide bombing by a Saudi man on a Shia mosque in neighbouring Kuwait last month, Saudi state news agency SPA reported on Tuesday.

The ultra-radical Sunni Islamic State group said it carried out the attack, which killed 27 people and appeared aimed at stoking sectarian hatred in the energy-rich Gulf.

The three Saudi brothers, who were not identified, were “parties to the crime of the sinful terrorist bombing that targeted the Imam al-Sadeq mosque in Kuwait”, SPA quoted a security spokesman for the interior ministry as saying.

One was arrested in Kuwait and will be extradited to the kingdom, another was arrested in the western Saudi city of Taif and a third was taken into custody after a shootout at a house near the Kuwaiti border that wounded two policemen. A fourth brother lives in Syria and is a member of Islamic State, the security spokesman added.

The bombing was Kuwait's deadliest militant attack, and the most lethal in any of the six hereditary-ruled Gulf Arab states since a campaign of al Qaeda bombings was stamped out in Saudi Arabia a decade ago.

Read more: Islamic State weaves web of support in Gulf Arab states

The attack has raised concerns about the number of young Saudi men willing to travel to carry out sectarian attacks in smaller Gulf Arab states and so make good on a threat by Islamic State to step up violence in the holy fasting month of Ramazan.

The group claimed two suicide bombings carried out on May 22 and May 29 on Shia mosques in eastern Saudi Arabia, where the bulk of Saudi Arabia's Shia minority lives.

Read more: Kuwait attack shows Gulf vulnerability to Islamic State