A court in Indonesia has handed sentences of less than six months to two men for their roles in an mob attack that killed three members of a minority religious sect.

Human rights groups criticized the sentences, saying they were far too lenient to discourage future violence by religious extremists.

The court Thursday gave a three-month sentence for manslaughter to Dani bin Misra, a 17-year-old who was seen in a widely distributed video striking a man in the head with a large stone as he lay on the ground. Idris bin Mahdani, who led about 1,000 people in the mob attack, received five and a half months for illegal possession of a machete.

The attack in early February targeted members of the Ahmadiyah Islamic sect, which is despised by hard-line Muslims because its members believe Mohamad was not the last prophet.

Three sect members were killed and at least eight were injured in the assault, in which the mob surrounded a house and attacked its 21 occupants with planks and machetes. A video of the attack was circulated on the Internet, showing about 30 policemen retreating ahead of the crowd.

Local reports said the sect members had been guarding the house after its owner was detained by police on suspicion he had been proselytizing.

President Susilo Bambang Yudhoyono later pledged there would be a full investigation.