Thailand's former premier Abhisit Vejjajiva (pic) is set to be charged with murder on Thursday over the death of a civilian during a military crackdown on anti-government "Red Shirt" rallies two years ago.

Abhisit, along with his then deputy Suthep Thaugsuban, will be formally charged at Bangkok's Department of Special Investigation (DSI), making them the first officials to face court over Thailand's worst political violence in decades.

About 90 people were killed and nearly 1,900 wounded in a series of street clashes between demonstrators and security forces, which culminated in a deadly army operation to break up the protest in May 2010.

The charge against Abhisit, who was prime minister at the time of the unrest, relates to the fatal shooting of taxi driver Phan Kamkong.

DSI chief Tarit Pengdith announced the move last Thursday and said it was prompted by a court's ruling in September that Phan was shot by troops -- the first completed inquest into the bloodshed.

Abhisit dismissed the case against him as "political" and said his government had no choice but to take tough action.

A terrorism case against 24 Red Shirt leaders, including five current lawmakers, is also set to begin on Thursday over their part in the rallies, which drew around 100,000 people at their height.

One of the accused, deputy commerce minister Nattawut Saikur, on Wednesday told AFP that he would not attend the hearing because he was required 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.

Sitting lawmakers have immunity so hearings can only be held when parliament is not in session, which is expected to further prolong the legal process.

The Red Shirts -- mostly supporters of ousted Thai premier 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.

Polls in 2011 brought Thaksin's Red Shirt-backed Puea Thai party to power with his sister Yingluck as premier, sweeping Abhisit into opposition.

In an interview before the charge against him was announced last month, Oxford-educated Abhisit told AFP that he was "not above the law" and would insist on his innocence in any prosecution.

"I've expressed my regret but I think a lot of people understand how much effort I put in to avoid losses. But it was the job of the government of that day to also restore order in the capital, in the country," he said.