BANGKOK, Thailand — Thailand's prime minister on Thursday ordered a state of emergency lifted in six provinces, but kept the decree in place in the capital Bangkok and nine other provinces.

Prime Minister Abhisit Vejjajiva did not explain why the emergency decree was revoked for the six provinces in the northeast and central Thailand. The state of emergency was declared in April after protesters in Bangkok broke into the parliament building to press their demands for early elections. About 90 people died and more than 1,400 were injured during two months of protests.

Deputy Prime Minister Suthep Thaugsuban said authorities considered the security situation in the remaining provinces to be tense and "actions that signalled some danger" persisted.

On Sunday, in the first major violent incident since the protests were quashed on May 19, a grenade exploded in downtown Bangkok, killing one person and wounding 10. No one has taken responsibility for the blast, which took place the same day as a parliamentary byelection in which a member of Abhisit's ruling Democrat Party defeated a candidate for a party that had backed the protests.

A state of emergency allows the government to impose curfews, prohibit public gatherings, censor and ban publications, detain suspects without charge, confiscate property and tap telephones, among other provisions.

Four out of the six provinces where the decree was lifted are in the northeast -- the stronghold of former Prime Minister Thaksin Shinawatra, who was ousted in a 2006 military coup amid allegations of corruption. Thaksin's supporters and their anti-coup allies, known as the Red Shirts, staged the street protests that ended violently when the army was sent in to disperse them.

The state of emergency was initially declared in Bangkok and later extended to cover almost one-third of the country's 76 provinces.

Local and international human rights advocacy groups have urged the emergency decree be lifted, expressing concern over provisions that allow extended detention, and saying its cessation would pave the way for true reconciliation.