Three men were shot dead early on Saturday, while a fourth was stabbed to death late on Friday in three southern provinces near the Malaysian border.
Waeseri Baka, 28, was stabbed to death in Tak Bai district in Narathiwat province as he walked through a coconut plantation, police said.
Early on Saturday, two armed men walked up to the gate of the Raman district hospital in Yala province and fired two shots at 53-year-old guard Nit Thongkongpan, police said.
The police, who blamed the attack on Muslim separatists, said he was pronounced dead at hospital.
Three Thai provinces near the Malaysian border have suffered almost daily attacks since separatists launched an insurgency in January 2004, killing 610 people, and the government of Thaksin Shinawatra responded with an iron fist.
Two men riding a motorcycle shot dead Makata Tuerosoh, a 50-year-old retired navy official, in the provincial town of Pattani around 6.20am local time (2320GMT) on Saturday.
The victim was riding a motorcycle with his wife on their way to buy food at a market when he was shot twice in the head, police said.
Violence in Thailand's south has
complex socio-political origins
Pichit Saelue, 57, a villager in Sungai Kolok in Narathiwat, was shot in the back and killed in front of a school also while riding a motorcycle on his way to market, police said.
Sungai Kolok was the scene of the deadly 17 February car bomb that killed six people and wounded 38 in the first such attack in the region.
Another man was shot and injured on Friday while taking an outdoor shower at his home in Rangae district in Narathiwat, police said.
A bomb exploded early on Friday in Si Sakhon district in Narathiwat province, police said.
However it failed to detonate properly and missed its apparent target – a truck carrying teachers and escorted by four Thai soldiers. No one was hurt in the blast.
Narathiwat is one of four southern provinces - the others being Yala, Pattani and Songhkla - where Muslims outnumber Buddhists in this country of 60 million people.
In April last year, clashes left more than 100 young local Muslims dead. Tensions escalated further after 86 Muslim protesters died, 78 of them by suffocation, when Thai security forces broke up a protest in southern Narathiwat on 25 October 2004.
The tragedy triggered international concern and widespread accusations that the government had used excessive force to quell protests. Subsequently, a government-appointed inquiry commission held three senior Thai officials responsible for the deaths and said action should be taken against them.