A string of grenade blasts shook a northern Thai city popular with foreign tourists, leaving several people wounded in attacks that police said Saturday could be linked to the kingdom's deadly political crisis.
The explosions in Chiang Mai on Friday evening came hours after the Constitutional Court nullified a February general election disrupted by opposition protests, angering government supporters.
The targets were a seafood restaurant, a petrol station and a brewery that has faced criticism because of its controlling family's links with anti-government protesters.
Four people were wounded but were out of danger Saturday and had returned home, Chiang Mai provincial police commander Grit Gitilue said by telephone.
"We established two possible motives for the attacks -- personal conflict or politics. We are giving more weight to the second one," he said, adding that no suspects had been arrested.
Two grenades were also fired near an anti-government rally in the eastern province of Chonburi on Friday evening but nobody was hurt, police said.
The unrest is a blow to efforts to lure back tourists after a state of emergency was recently lifted in Bangkok in response to an easing of months of political violence that has left 23 people dead.
The violence, mostly concentrated in Bangkok, has often targeted opposition protesters seeking to topple Prime Minister Yingluck Shinawatra's government and install an unelected "people's council" to oversee reforms.
Thailand has been bitterly divided since her elder brother Thaksin Shinawatra was ousted as premier by royalist generals in a 2006 coup.
Yingluck has been charged with negligence in connection with a rice subsidy scheme, and could face impeachment within weeks.
Her supporters, known as the "Red Shirts", have warned that they will not tolerate a "judicial coup" to oust the government through the courts.
The red-clad movement was due to hold a political rally on Saturday evening in the seaside city of Pattaya.
Their mass protests against the previous government in 2010 triggered street clashes and a military crackdown that left more than 90 people dead in the country's worst civil unrest in decades.
Yingluck's Puea Thai Party had been expected to win the February election, which was boycotted by the opposition.
The polls were annulled on the grounds that they were not held nationwide on the same day, due to the disruption by demonstrators.
Parties linked to Thaksin -- who lives in Dubai to avoid prison for corruption -- won every previous election for more than a decade, helped by strong support in the north.
But many southerners and Bangkok residents accuse the Shinawatra family of raiding the public coffers to buy the loyalty of rural voters through populist policies.