Thailand will keep 18 of its provinces and its capital city under a state of emergency for the next three months as the government tries to keep a lid on the unrest that fuelled waves of violent protests earlier this year.

Ongart Klampaiboon, the minister to the Prime Minister's Office, told reporters that the Thai cabinet believes there are "situations that require close monitoring and surveillance" in Bangkok and the 18 provinces where the emergency law was extended.

The government also lifted the restrictions in five other provinces.

Critics say the contentious emergency laws give the prime minister too much power, allowing him to overrule any civilian or military agency owned by the state.

The emergency laws also allow officials to arrest and detain people for up to 30 days, in a process that exists outside the regular judicial system. Under this arrangement, detainees are not guaranteed legal representation, nor visits from family members.

"Thailand has never seen this kind of situation," said Sunai Phasuk, a senior researcher for the New York-based Human Rights Watch.

"A large number of protesters have been detained but no one knows the exact figures, or even their whereabouts."

Anti-government demonstrations lasted for weeks in Bangkok, as the so-called Red Shirt protesters took to the streets of the Thai capital through much of April and May.

Loyal to former Thai prime minister Thaksin Shinawatra, the Red Shirts called for the resignation of incumbent Prime Minister Abhisit Vejjajiva and refused to back down.

Eventually, the Thai government sent troops into a part of Bangkok where the protesters were camping. They dismantled the camp -- which was essentially a fortified city -- and broke up the demonstrations.

Many of the Red shirt leaders were arrested and some have been charged with terrorism.

Some 1,400 people were injured during the nine weeks of protests and nearly 90 people were killed.

Thailand has seen sporadic violence flare up at various points across the country since the government forced an end to the Red Shirt protests on May 19.

With files from The Associated Press