One person was killed and three others wounded after an unidentified gunman opened fire on demonstrators in Bangkok as a key phase of the election began on Saturday.
The shooting took place around 3:30 am (4:30 am Singapore time) close to government house and near the protesters' permanent rally site.
The incident came barely 48 hours after clashes between police and protesters.
The slain victim was a member of a student group allied to the anti-government People's Democratic Reform Committee (PDRC) which has been trying to derail the election.
The incident brought the death toll in election-related violence to three and the number of those injured to over 150 since Thursday.
Anti-government protesters of the self styled People's Committee for Democratic Reforms (PDRC) led by politician Suthep Thaugsuban, have been trying to derail the election process, and force acting prime minister Yingluck Shinawatra to resign.
Mr Suthep is demanding that an appointed "people's council" be set up to run the country for a year, and institute reforms, before another election can be allowed.
The opposition Democrat Party is also boycotting the election, saying it will not solve Thailand's bitter political crisis pitting supporters of former prime minister Thaksin Shinawatra - older brother of current premier Yingluck Shinawatra - against a largely Bangkok-centric royalist middle and upper middle class.
But the beleaguered government run by Mr Thaksin's proxy party, the Puea Thai - which won a comfortable majority in the last election in 2011 - is determined to hold elections on Feb 2.
At least until Saturday afternoon, there were no protesters in evidence at the registration venue in a sprawling government complex in Bangkok, where registration of individual candidates commenced.
But in at least six other provinces, Election Commission officials came under pressure from protesters and had to call off the registration exercise.
Up north, no violence was reported as the process got underway in Chiang Mai, the stronghold of the Puea Thai party and hometown of the Shinawatra clan.
Ms Yaowapa Wongsawat, Mr Thaksin's sister, will not contest her seat in 2014, it was announced. Instead her son Yodchanan Wongsawat, a 35 year old assistant professor at Mahidol University, will contest her seat.
Registration will continue throughout the country till next Wednesday.
On Friday, deputy prime minister Surapong Tovichakchaikul said the government would ask the army for help in ensuring security for the election.
And on the same day army chief, General Prayuth Chan-ocha, who has been careful not to appear to take sides, repeated a call for restraint and for the first time said a military takeover could be on the cards.
The army has launched 18 coups or attempted coups since 1932 when Thailand became a democracy under a constitutional monarchy.
The police force, under orders to show restraint to avoid a situation in which the government is seen to be using too much force, is becoming increasingly frustrated.
This showed on Thursday when some police units reacted with rage and got into pitched battles with protesters armed mostly with rocks and slingshots.
One of the first to register as an election candidate in Bangkok this morning was Dr Poowanida Kunpalin, from the Puea Thai party.
A four-time MP, the 45 year old told The Straits Times she was concerned about violence during the campaign.
"We hope the police and the army can keep the country at peace," she said.
- with additional reporting by Tan Hui Yee in Chiang Mai
