The attacks came as the deputy prime minister visited the region, officials said on Thursday.
Initial reports showed that 21 homemade bombs were detonated, Kongsak Wanthana, the interior minister, said.
At least 16 people were injured in the blasts that went off between 8.30am (0130 GMT) and 9am, as people headed to work in the three Muslim-majority provinces of Narathiwat, Pattani and Yala, said Boonyasit Suwanarat, the governor of Yala.
Many of the bombs were planted inside bathrooms of provincial town offices and police stations, injuring three police officers in Yala province and five marines in neighbouring Narathiwat, Korkiat said.
One of the bombs went off at a government office in Yala minutes before Chitchai Wannasathit, the deputy prime minister, was due for a visit in the area. Chitai is in charge of overseeing security in Thailand's south.
Both fatalities occurred in Pattani province. A blast at the provincial town hall killed a security officer.
Separately, a local official was killed by a bomb that went off at a tea shop known to draw a morning crowd of government employees, said Police Major-General Korkiat Wongworachat.
Jamming phone signals
The authorities jammed mobile phone signals in the area to prevent insurgents from using mobiles to detonate more bombs, Korkiat said.
Thaksin Shinawatra, the prime minister, said that intelligence had indicated insurgents were planning a "major operation" for Thursday but the government's security prevention network was "not good enough" to block the attacks.
The Thai prime minister said
security was not good enough
"Chitchai is in the areas now to inspect the situation," Thaksin said, adding that he too, planned to visit the region soon.
The insurgents, who have made no public demands but are believed to favour independence from majority Buddhist Thailand for the country's three southernmost Muslim provinces, often attack symbols of state authority.
More than 1,300 people have been killed since violence flared in early 2004.