Security forces have killed at least 100 suspected Islamic militants in a spate of gun battles in south Thailand.
Police said they were tipped off the attackers were coming
At least 30 died in a raid on a mosque where they were taking refuge from clashes with the army, officials said.
Others died during scuffles near police bases, which the attackers stormed in a series of co-ordinated attacks.
Thailand's prime minister has blamed local gangs, but many officials fear international militant groups may be behind the attacks.
The BBC correspondent in Bangkok, Kylie Morris, says the fighting is a serious escalation of the violence that began in early January with a raid on a military arsenal.
In the intervening months, more than 100 people have been killed in almost daily small-scale attacks.
Wednesday's violence took place in the three Muslim-dominated provinces of Thailand - Yala, Pattani and Songkhla.
Yala: At least 5 police posts attacked
Songkhla: 1 security base targeted
Pattani: Shoot-out between police and gunmen trapped in mosque
Police in Yala said the attackers were mainly young men, armed with guns and machetes.
They carried out a series of co-ordinated attacks on police bases and village defence posts in the region, security forces said.
Although officials were tipped off to expect the dawn attacks, few would have envisaged their scale, our correspondent says.
Abdulrazak Ali, a local Islamic committee leader, told the BBC: "I have never dreamed that such a serious incident could take place here. It's unprecedented - so many deaths in one day."
"We are sorry that those youths had to lose their lives because, as the authorities said, they were misled by those with ill intentions," he said.
Clashes took place near 10 police outposts around the southern provinces. One particularly bloody battle erupted in the Krue Se mosque in Pattani - where up to 38 people reportedly lost their lives.
Police fired tear gas and rocket-propelled grenades into
the mosque, village headman
Waedaloh Hayeesohoh told the Associated Press news agency.
One man had JI on his shirt, raising fears of international terrorist links
Five security personnel are said to be among those killed in Wednesday's violence, compared with more than 100 insurgent deaths.
Prime Minister Thaksin Shinawatra said the toll among security forces was low because the militants had only been armed with machetes and a few guns.
He described those who carried out the attacks as "youths from the southern provinces" whose actions were "not linked with international terrorists".
But some analysts have voiced concerns that the attackers could have links to militant groups outside Thailand.
One of the men killed in Wednesday's violence was found to be wearing a shirt with JI emblazoned on the back - a possible reference to Jemaah Islamiah, the group blamed for terrorist
attacks across South East Asia, including the Bali bombings.
Many observers say the current troubles in Thailand's south have been exacerbated by the government's own policy of cracking down on militants.
Islamic community leaders say the tactics employed by security forces have been heavy-handed, and may have served to encourage those who already felt disenfranchised.
The alienation felt by Thailand's Muslim minority has been the source of a decades-old separatist struggle, which decreased in intensity after an amnesty in the late 1980s but resurfaced again this January.
Thailand is predominantly Buddhist, with its 4% Muslim population concentrated in the troubled southern provinces - Pattani, Yala, Songkhla and Narathiwat.