Twenty-eight people have been injured, seven of them seriously, in an explosion at a camp of anti-government protesters in the centre of Bangkok.
It is the second such assault in recent days on demonstrators staging "shutdown" protests aimed at toppling the Thai government.
Unknown attackers have killed several people during the months-long demonstrations intended to oust the embattled government of Prime Minister Yingluck Shinawatra.
Each side has blamed the other for the violence.
Today's attack, twin blasts followed by gunshots at a busy intersection occupied by the protesters, heightened fears of growing violence before elections called by Ms Yingluck for 2 February.
A protest leader told reporters "an explosive device" was thrown into a crowd near a tent where he was sitting behind the main rally stage.
An AFP reporter saw blood-spattered clothes and a small crater at the scene of one of the blasts.
Those injured were taken to several city hospitals after the attack, a health official said.
The capital's Erawan emergency centre confirmed the casualties, adding in an update that nine of the 28 were later released from hospital.
The leader of the rallies said protesters would not be cowed by violence and vowed to extend the action across the southern provinces tomorrow.
Thailand has been rocked by bouts of bloody unrest since just before a 2006 military coup that ousted Prime Minister Thaksin Shinawatra.
He now lives in self-exile overseas to avoid a jail term for corruption.
His younger sister Yingluck has clung on to power through more than two months of street rallies aimed at forcing her elected government from office and installing an unelected "people's council".
She has called the elections despite a vow by the main opposition party to boycott them and threats from the protesters to disrupt the polls.
The demonstrators have staged a self-styled "shutdown" of the city since last Monday, erecting roadblocks and rally stages at several intersections including those in its commercial heart.
The action has brought inconvenience to the city of 12 million, but authorities say the numbers on the streets appear to be dwindling - although tens of thousands join nightly rallies.
The demonstrators are urging the military and independent institutions to bolster their attempt to block the election, which Ms Yingluck is again expected to win.
Observers say widespread violence could prompt intervention by the powerful army in a nation that has seen numerous attempted or successful coups since it abandoned absolute monarchy in 1932.
Yesterday one protester died and dozens were injured in a blast at an anti-government march in the city.
Police today said they were hunting two suspects captured on CCTV footage leaving the scene of Friday's attack after joining the march.
The current wave of protesters is made up of a coalition of Mr Thaksin's foes among the Bangkok middle class, southerners and the pro-royalist elite.
But the ousted leader has strong support in the north and northeast, which has helped him or his allies win every election in Thailand this century.