Sant Rama Nand, the head of a leading Indian Sikh sect who died of a temple wound in an assault by members of a rival fundamentalist group, was killed in a 'planned attack', Vienna [Images] police said on Monday.

"The attack had clearly been planned," police spokesman Michael Takacs told media persons, adding that a full investigation was on in the case in which at least 16 people were wounded, some of them seriously.

The attack has sparked off widespread riots in parts of northern India, where the followers of Sant Rama Nand, associate head of the Jalandhar-based Dera Sacha Khand, took to the streets to protest the killing of the preacher.

Nand, 57, one of the two visiting preachers died of his wounds in hospital.

Six of the attackers, who were later apprehended and roughed up by the devotees, are also lodged in hospital. The condition of four of the attackers was serious, while the other two were stable and were questioned by the police.

The Austrian police did not rule out the possibility of more arrests.

"The investigations are continuing to find out if the six attackers were acting alone or under orders," the spokesman said.

Police revised the number of injured in the attack from about 30 to 16. The other preacher Sant Niranjan Dass, 66 is among the seriously injured.

Takacs said the attackers who pulled out knives and fired from a gun on Sunday as the 'Sant' was preaching to about 200 disciples at a gurdwara near Vienna, were Indian nationals who were living in Austria for some time.

The gurdwara where the attack occurred is located in Vienna's 15th district. Some 3,000 Sikhs live in Austria. The police spokesman said Sant Anand underwent an emergency operation but "lost consciousness and died shortly after midnight on Sunday."

Takacs said the six people who opposed the sermon had launched the attack. "One drew a firearm, the others knives. The six people were overpowered by members of the community and seriously injured."

Two of the wounded attackers were in critical condition after being shot in the head, he said. The gurdwara, that witnessed the clash, was opened in Vienna in December 2005.