QATIF: Saudi Arabia's Shia minority prepared a mass funeral Monday for the victims of a mosque bombing that authorities described as an attempt by Sunni extremists to sow sectarian strife.

Take a look: Deadly suicide blast at mosque in Saudi Arabia kills 21

Organisers said they expected huge crowds to turn out in the mainly Shia Qatif district of Eastern Province to show their respects for the 21 dead, who included two children.

Everybody “is very much anxious to participate... to express their support,” one organiser said, asking not to be named.

Last Friday's suicide bombing, during the mainly weekly Muslim prayers in Kudeih village, was the second mass killing of Shias in the kingdom since late last year.

In November, gunmen killed seven Shias in the Eastern Province town of Al-Dalwa.

Asked whether he feared a new attack during the funeral, the organiser said: “Nobody can predict anything. We have taken all precautions in coordination with local authorities."

He added that tens of thousands of people had volunteered to act as crowd marshals for the three-hour ceremony.

He said safety concerns had prompted organisers to ask women to stay away from the funeral but that a separate area had been set up for them to offer condolences after the burials.

The Islamic State group said it carried out the bombing, the first time the jihadists, who control swathes of neighbouring Iraq and Syria, had claimed an attack in the Sunni-dominated kingdom.

The interior ministry confirmed that the bomber, a Saudi national, had links with IS, which considers Shias heretics.

It was the deadliest attack in years in Saudi Arabia and King Salman vowed on Sunday that anyone with the slightest involvement in the “heinous crime “would be punished.

Read: Saudi king vows to punish those behind suicide attack in Shia mosque

Most of the kingdom's Shias live in the east, where the vast majority of the kingdom's oil reserves lie but where Shias have long complained of marginalisation.

Saudi Arabia and its Sunni Gulf neighbours joined a US-led air campaign against IS in Syria last year, raising concerns about possible retaliation in the kingdom.