* One protester shot dead, four hurt - emergency officials
* PM faces possible impeachment over negligence charges
* Pro-government "red shirts" to rally on Saturday, raising risk of confrontation (Recasts)
By Amy Sawitta Lefevre
BANGKOK, April 1 (Reuters) - Gunmen opened fire on a group of Thai anti-government protesters driving away from a Bangkok rally on Tuesday, killing one, wounding four and raising tension in a political crisis that has gripped the country for months.
It was not immediately clear who was responsible for the violence which brought the death toll to 24, with scores wounded, since protesters took to the streets in November in a bid to force Prime Minister Yingluck Shinawatra from office and erase the influence of her brother, ousted premier Thaksin Shinawatra.
Yingluck has resisted mounting pressure to step down and her "red shirt" supporters have called for a mass rally in Bangkok on Sunday, raising the risk of further confrontation..
"We received three (of the) injured protesters at the hospital. One succumbed to a gunshot wound to the head," an official at Ramathibodi Hospital in Bangkok told Reuters.
In a rare piece of good news for Yingluck, who is battling negligence charges brought by the national anti-graft commission, unofficial results of Thailand's weekend Senate election suggest a pro-government majority.
Yingluck has been charged with dereliction of duty for her role in overseeing a disastrous state rice-buying scheme that has run up huge losses. Should the National Anti-Corruption Commission (NACC) forward the case to the Senate for possible impeachment, she could be removed from office.
That would require the votes of three-fifths of the senators. Thailand's 150-seat Senate is made up of 77 elected senators. The other 73 are appointed and are largely seen as opponents of the government.
Preliminary results released by the Election Commission on Monday show winning candidates in the north and northeast, Thaksin strongholds, are largely linked to the ruling Puea Thai Party and Thaksin's now-defunct Thai Rak Thai party.
"Definitely the names we're seeing on the list of winners are mostly pro-government, with ties to the ruling party and coalition party," Paiboon Nititawan, an appointed senator who has sided with anti-government protesters in the past.
"It is not possible that the Senate will get the three-fifths of votes needed to remove the prime minister."
While the Senate is officially non-partisan, the majority of the 77 elected seats were likely decided on the basis of endorsements from powerful, party-affiliated institutions.
It remains unclear when the NACC will decide whether to forward Yingluck's case to the Senate, dragging out weeks of uncertainty and leaving Yingluck at the helm of a caretaker government with limited powers.
And there is a further legal challenge. A group of 27 senators has petitioned the Constitutional Court to rule that her removal of National Security Chief Thawil Pliensree in 2011 violated the constitution. A court ruling reinstated him last week.
The Constitutional Court will decide on Wednesday whether to accept the case.
"The anti-government side are plotting different ways to remove the government," said political analyst Kan Yuenyong at Siam Intelligence Unit think-tank.
"They will go at it from every angle they can, throwing legal challenges at the prime minister until one sticks."
Yingluck defended herself on Monday against the negligence charges and asked for time to submit evidence in her defence. The commission extended the deadline on Tuesday but has yet to specify a time frame.
Protesters first took to the streets to oppose an amnesty bill that critics said would have allowed for Thaksin's return from self-exile. The bill was eventually rejected by the Senate but protests continued and new demands emerged.
Thailand has really been in crisis since Thaksin was ousted in a 2006 coup. The conflict broadly pits Bangkok's middle class and conservative establishment against Yingluck and Thaksin's supporters in the north and northeast.
Protesters disrupted a Feb. 2 general election, halting voting in parts of Bangkok and the south. The Constitutional Court nullified the election last month, throwing Thailand into deeper turmoil and leaving Yingluck in charge of a caretaker government with severely restricted powers.
The protesters want to set up a "people's council" of unspecified worthy people to force through political and electoral changes before a new general election is held. (Additional reporting by Aukkarapon Niyomyat: Editing by Nick Macfie)