BANGKOK (AFP) - Thousands of anti-government "Red Shirts" gathered in Bangkok on Sunday to mark a year since deadly clashes between troops and protesters during their mass rally in the capital. Police said about 20,000 had gathered by nightfall - decked in their signature scarlet garb, with banners and handclappers - although an AFP reporter estimated the crowd size at nearer 30,000, undeterred by rainfall. Fugitive former prime minister Thaksin Shinawatra, a hero for many of the demonstrators, was due to address the crowd via video link during the rally, which was expected to go on late into the night. Thailand, which is preparing for elections set to be held later this year, remains deeply divided following the worst civil violence in decades in April and May 2010 that left more than 90 people dead, mostly civilians. Fights between the military and protesters on April 10 last year left 26 people dead and marked a violent turning point in the rally. The protest was halted the following month, when troops firing live rounds and backed by armoured vehicles moved in to disperse the demonstrators. The Reds began Sunday's year-on demonstration with a religious ceremony at which monks prayed for the dead and relatives held pictures of their loved ones who were killed. They later held a one-minute silence in commemoration. "The purpose of the rally Sunday is to mark the first anniversary of the brutal crackdown on unarmed protesters, and we want to honour our heroes," said Red Shirt spokesman Worawut Wichaidit. Among those killed on April 10 was Hiro Muramoto, a 43-year-old Japanese cameraman working for news agency Reuters. Thai police last month said there was no evidence to show troops were responsible for his death, despite initial findings by the Department of Special Investigation that suggested they might have been. "Today we pay tribute to Hiro's life, but remain discouraged that the circumstances of his death are still unknown a year later," said Stephen Adler, Reuters editor-in-chief. "Hiro's family and Reuters colleagues deserve to know how this tragedy occurred and who was behind it." Both military and protesters accused each other of using live ammunition during last year's clashes. Recent Red Shirt gatherings have attracted tens of thousands of protesters to the capital and marked a show of strength for the movement, but have been well short of the 100,000 people who joined last year's protests at their peak. Major General Wichai Sungprapai, of the Bangkok Metropolitan Police, said that around 3,300 officers would be deployed for Sunday's demonstration, which had been expected to swell to crowds of 50,000. The Reds view Prime Minister Abhisit Vejjajiva's government as an unelected elite because it came to power in a 2008 parliamentary vote with military backing, after a court ruling threw out the previous administration. "We don't fight for ourselves but for all Thais, for the younger generation to have equality in life," said one of Sunday's banners waved on the streets. Thaksin, who was ousted in a 2006 coup and now lives abroad to avoid a jail term for corruption, was set to address the crowd from overseas in the evening, according to Red Shirt Nattawut Saikua. A former billionaire telecoms tycoon, Thaksin is hailed by the Reds for his policies for the poor while in power, but seen by the Thai ruling elite as authoritarian, corrupt and a threat to the revered monarchy. He faces terrorism charges in Thailand, accused of bankrolling last year's anti-government protests and of instigating unrest.