A gunman opened fire on an opposition rally in the Thai capital early Saturday, killing one person and wounding three others in an incident that could inflame political tensions in the country.
Some witnesses say the shots were fired from a passing car into a group of protesters camped overnight near the government house in Bangkok.
Meanwhile, anti-government protesters surrounded candidate registration locations in the country's opposition-dominated south, forcing officials to suspend the sign-up process in some provinces.
Early elections are scheduled for February 2.
The developments follow weeks of protests by people seeking to oust Prime Minister Yingluck Shinawatra. Demonstrators say her removal is necessary to purge the country of corruption and money politics.
Thai anti government protesters rally next to riot policemen during the registration of constituency candidates in Nakhon Si Thammarat, Dec. 28, 2013.
Riot policemen walk around during a registration of election candidates at a bus terminal centre near the Government complex in Bangkok.
Photographs of Poowanida Kunpalin from the ruling Puea Thai Party are seen as her documents are inspected during a registration of election candidates at a bus terminal centre near the Government complex in Bangkok.
Election commission officers and candidates gather during a registration of election candidates near the Government complex in Bangkok.
A Thai anti-government protester cries and takes picture during a condolence ceremony for Yuthana Ong-art, who was shot and killed on Friday night, in Bangkok, Thailand.
Thai anti-government protesters mourn in front of the picture of Yuthana Ong-art, who was shot and killed on Friday night, during a condolence ceremony in Bangkok, Thailand.
Thai anti-government protesters chat outside a makeshift camp where their colleagues were shot outside the prime minister's office of Government House in Bangkok, Thailand.
Thai anti-government protester washes his face at a protest site outside the Government House in Bangkok.
In a televised address Friday, Army Chief General Prayuth Chan-ocah declined to rule out the possibility of a coup in Thailand. Prayuth also repeated a request that people stop asking the army to take sides in the bitter dispute.
Demonstrators view Yingluck as a puppet of her brother, former Prime Minister Thaksin Shinawatra.
Large protests have forced her to call for early elections and dissolve parliament, but she has refused to resign.
Former prime minister Thaksin, a billionaire businessman, was ousted in a 2006 military coup. He was convicted of corruption and lives in self-imposed exile.