(Removes extraneous word in paragraph 2, typographical error paragraph 5)
* Unidentified gunman opens fire in pre-dawn attack
* Protesters block election registration centres in southern provinces
* Military has not ruled out intervention
By Sinthana Kosolpradit
BANGKOK, Dec 28 (Reuters) - A Thai protester was killed and four wounded on Saturday, an emergency official said, when an unidentified gunman opened fire on demonstrators whose efforts to topple Prime Minister Yingluck Shinawatra have flared into violence in recent days.
The shooting came 48 hours after clashes between police and the protesters, who are determined to disrupt a snap Feb. 2 election called by Yingluck, outside a voting registration centre in which two people were killed and scores wounded.
The violence is the latest in years of rivalry between Bangkok's middle class and royalist establishment and the mostly poor, rural supporters of Yingluck and her brother, Thaksin Shinawatra, a populist former premier who was ousted in a military coup in 2006 and lives in self-imposed exile.
Petphong Kamjonkitkarn, director of the Erawan Emergency Centre in the capital, Bangkok, told Reuters one man in his 30s had been shot dead. Four suffered gunshot wounds.
The protesters have been rallying for weeks in their attempt to topple Yingluck, who they see as a puppet of her brother, and they have vowed to block an election that Yingluck would most likely win.
Yingluck, who draws her support from the rural north and northeast, is determined to go ahead with the poll. On Friday, her government asked the military for help to provide security for candidates and voters.
However, the chief of the heavily politicised army declined to rule out military intervention, responding that "the door was neither open nor closed" when asked if a coup was possible.
Several hundred protesters are camped out in tents around the walls of Yingluck's Government House offices, one of several rally sites around the capital. Witnesses said they were sleeping when gunfire rang out at about 3.30 a.m. (2030 GMT Friday).
"I was sleeping and then I heard several gunshots. I was surprised," said one 18-year-old protester, who identified himself by his nickname "Boy".
Other witness said the shots could have come from a car as it drove past the protest site. Reuters television pictures showed bullet holes in a concrete barrier and a generator, as well as bloodstains inside a tents.
Protesters showed several small-calibre slugs they found.
SOUTHERN CENTRES BLOCKED
Registration for the election was to continue on Saturday, although the Election Commission (EC) has asked that the poll be delayed after Thursday's violence until "mutual consent" from all sides was achieved - a very unlikely scenario.
EC Secretary-General Puchong Nutrawong told Reuters the commission had temporarily closed registration centres in six southern provinces because the sites had been blocked by protesters and candidates hoping to register could not enter.
Media reported that protesters had cut water and electricity to some of the sites.
The protesters draw much support from the south, as does the main opposition and pro-establishment Democrat Party, Thailand's oldest party. It has further muddied the waters by saying it will boycott the poll.
With the street protests escalating, any delay to a poll that Yingluck's Puea Thai Party would otherwise be expected to win would leave her government open to legal challenges or military or judicial intervention.
The military has staged or attempted 18 coups in 81 years of democracy, making Friday's comments by General Prayuth Chan-ocha more chilling for Yingluck and Thaksin.
The protesters draw strength from Bangkok's conservative middle class, royalist bureaucracy and elite, many with ties to the judiciary and military, who resent the rise of the billionaire Shinawatra family and their political juggernaut.
They accuse former telecoms tycoon Thaksin of corruption and manipulating a fragile democracy by effectively buying the support of the rural poor with populist policies such as cheap healthcare, easy credit and subsidies for rice farmers.
Instead of an election, the protesters want an appointed "people's council" to oversee reforms before any future vote.
Thaksin's enemies also accused him of trying to undermine King Bhumibol Adulyadej. Thaksin denied that.
The first two years of Yingluck's government had been relatively smooth until a blunder by her party in November, when it tried to push through an unpopular amnesty bill that would have exonerated Thaksin from a 2008 graft conviction he says was politically motivated. Thaksin fled into exile shortly before he was sentenced to a two-year jail term. (Additional reporting by Jutarat Skulpichetrat, Viparat Jantraprapaweth and Kochakorn Boonlai; Writing by Paul Tait; Editing by Robert Birsel)