A man on a motorcycle hurled a home-made bomb at a hotel in Hat Yai yesterday but the device failed to cause any damage because it landed in a drain, police and eyewitnesses said.

No one was injured in the blast at the High End Hotel, but the fact that it came just a day after two similar incidents was a setback for security forces that have been on high alert since Sunday night when Hat Yai was hit by seven bomb attacks that injured 13 people.

One victim remained in critical condition after the Sunday attacks while another, Suchart Sae-tang, 60, passed away yesterday from head injuries.

On Monday evening, a bomb went off in a market in Songkhla's Sabai Yoi district killing four people and injuring 26.

Army spokesman Colonel Acara Tiproch blamed the Saba Yoi bombing on Muslim militants.

Saba Yoi's mayor, Cholada Niwaswutkij, called on the authorities to post more troops and Border Patrol Police to the district to boost security.

She said Monday's bombing was the worst incident of violence in the district for three years.

The call for more troops came just hours after a group of 30 armed youths went on a rampage in Saba Yoi shortly after midnight yesterday, firing automatic rifles and shotguns in the air for about 20 minutes and shouting that they had achieved "victory". No injuries were reported after the incident.

While officials said the Saba Yoi attack was part of the ongoing unrest in the Malay-speaking South, most officials have been reluctant to link the Hat Yai bombs to the ongoing insurgency in the region.

Lt-General Jetanakorn Napeetapat, a regional police chief, said he believed the bomb attacks in Hat Yai were "politically motivated".

The blasts come just ahead of the crucial court announcement in Bangkok affecting the future of Thailand's two main political parties.

Meanwhile, in Pattani's Ban Tanyong Luloh district, village chief Wae-soha Haji-soha, 54, was shot dead by three gunmen riding on a motorbike.

The gunmen also stole his 11mm handgun, said Roteepah Mamah, 45, Wae-soha's wife, who was riding pillion on his motorbike at the time of the attack. She suffered injuries to her arms as a result of the crash.

In Yala's Tambon Patae, about 50 police officers swooped on a local imam, Yunu Ma-ae, 54, and detained him for questioning in relation to the ongoing violence. His detention prompted about 100 local residents to stage protests in Yaha district calling for his release.