Abhisit Vejjajiva, the former prime minister of Thailand, has been charged with murder over the death of a civilian during a crackdown on anti-government rallies two years ago, his party says.
Abhisit, along with then-deputy Suthep Thaugsuban, was formally charged at Bangkok's Department of Special Investigation (DSI) on Thursday.
They are the first officials to face a court over Thailand's worst political violence in decades.
"The DSI has charged Abhisit and Suthep on section 288, which is murder. They both denied the charge," Thavorn Senniem, a senior Democrat Party lawmaker, told AFP.
Hundreds of riot police were deployed to guard the building, as about 20 supporters carrying roses and dozens of protesters holding pictures of those killed during the crisis watched the former leader arrive.
At least 90 people were killed and nearly 1,900 wounded in a series of street clashes between "Red Shirt" protesters and security forces. The crisis culminated in a deadly army operation in 2010 to break up the demonstrations.
The charge against Abhisit, who was prime minister at the time, relates to the fatal shooting of taxi driver Phan Kamkong.
Tarit Pengdith, the chief of the DSI, announced the move last Thursday, saying that it was prompted by a court ruling in September that Phan was shot by troops. That ruling was the first completed inquest into the 2010 bloodshed.
Abhisit dismissed the case against him as "political" and said his government had no choice but to take tough action. The rallies drew around 100,000 people at their height.
'Red Shirt' trial delayed
Meanwhile, a separate terrorism case against 24 leaders of the Red Shirts, including five current legislators, for their part in the rallies was postponed after two witnesses failed to attend.
"The court has postponed the hearing until [Friday]," a judge said, adding the court will issue an arrest warrant for one of the accused, deputy commerce minister Nattawut Saikur, if he is not present then.
Nattawut had said he would miss Thursday's court date because he had to accompany Prime Minister Yingluck Shinawatra on an official visit.
The trial against the Red Shirt leaders, who pleaded not guilty in August 2010, has been repeatedly postponed.
The Red Shirts - mostly supporters of ousted prime minister Thaksin Shinawatra - were demanding immediate elections in their 2010 protest.
They accused Abhisit's government of being undemocratic because it took office in 2008 through a parliamentary vote after a court stripped Thaksin's allies of power.
Elections in 2011 saw Thaksin's Puea Thai party come back to power, with his sister Yingluck taking the prime minister's post.