A bomb exploded near the Thai king's residence in Bangkok, wounding one person and sparking a security clampdown, police said.
Bangkok's police superintendent Lt Gen Adisorn Nontree said he had ordered an urgent security meeting for Sunday after the blast on a road opposite Chitralada Palace the previous evening. The king and most of the royal family were not staying at the palace at the time of the explosion.
A 22-year-old man was slightly wounded by the bomb which was hidden in a paper bag and placed on a road by a phone box, said police Lt Col Kritsadang Chittriphol.
"He saw a spark coming out of the paper bag and ran about 10 meters (32 feet) and then the bomb exploded," he said. The explosion shattered glass but was not powerful enough to kill a person, Kritsadang said.
"It is an attempt to cause chaos," he said, adding that it was not clear if it was related to politics or terrorism.
Police, bomb squads and bomb-sniffing dogs were rushed to the scene and authorities sealed off the area to vehicles and the public.
Extra security was thrown up around the palace. Chitralada Palace, set in an extensive, walled compound, used to be the prime Bangkok residence of King Bhumibol Adulyadej and members of his family, but in recent years the much revered constitutional monarch has been spending most of his time at a seaside resort.
Other family members live elsewhere. Thailand has been rocked by both political instability following a military coup last September which ousted Prime Minister Thaksin Shinawatra and a bloody Muslim insurgency in its southernmost provinces.
Nine bombs exploded in the Thai capital on New Year's Eve, killing three people and wounding more than 40. Authorities have yet to unravel the motives behind the attacks or arrest the perpetrators.