Fears that Buddhist schools in southern Thailand may be targeted by Islamic separatists have led some to shut.
Thailand's south remains tense
Education Minister Adisai Bodharamik said he had warned Buddhist teachers in the mainly Muslim south they could be swept up in the region's violence.
Schools have often been targeted during the unrest, which has seen more than 400 people killed this year.
In Bangkok, a fight broke out in the country's Senate between legislators regarding the violence.
Correspondents say that the clash is a symptom of how divided the country has become the issue of the south.
A government inquiry is currently investigating the deaths of dozens of Muslim protestors after they were taken into custody last week.
On Tuesday, police said a Buddhist village official in the southern province of Narathiwat had been beheaded in apparent revenge for their deaths.
The Muslims died after protesting outside a police station in Takbai, in the same province, to demonstrate against the detention of six Muslim men on weapons charges.
Dozens of Muslims youths were bundled into army vans without enough air to breathe and 78 perished. Seven others died during the protest itself.
A heated debate took place in Thailand's Senate on Wednesday about the incident, and two senators exchanged blows about who was to blame.
Abdul Wanchbaitanawong from the northern province of Mae Hong Son, said of critics of the government: "You guys have already talked too much, and in blaming the state authorities for overreacting, it seems that you guys are siding with the terrorists and sympathise with the bandits," he said.
Prathin Santhiprapob, a former police chief, responded by accusing politicians from northern Thailand of corruption.
He then punched his colleague in the face, and the pair had to be separated.
Thai Prime Minister Thaksin Shinawatra has ordered an independent panel to investigate the Takbai incident, and it will report its findings to the prime minister by 2 December.
Islamic leaders have warned that the deaths could trigger reprisal attacks in Thailand's south.
Last week, a statement issued by the local militant organisation Pulo (Pattani United Liberation Organisation) warned tourists to avoid the popular resorts of Krabi and Phuket, and the capital, Bangkok, in addition to the four southern provinces.
The UN has warned its staff to take the threat to Bangkok seriously, Reuters news agency said on Wednesday after seeing the contents of an internal email.
"It is entirely possible that an attack is being planned against a soft target in Bangkok," the note from the organisation's chief security officer writes, according to the agency.
The south of Thailand is home to most of the country's Muslim minority, which has long complained of discrimination by the authorities in Bangkok.
Many of this year's deaths have been blamed on Muslim militants targeting local officials, teachers and members of the security forces.