"It's a political game. The ruling Puea Thai party is forcing Mr. Abhisit and Mr. Suthep to accept the deal," said Siripan Noksuan Sawasdee, a political-science professor at Chulalongkorn University.

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The attorney general's office denied that the indictment was politically motivated. The office received requests for indictment by the Department of Special Investigation—the Thai version of the U.S. Federal Bureau of Investigation—in June, following a probe late last year.

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About 90 people, mostly "red shirt" street protesters, were killed when crowds occupied downtown Bangkok for nine weeks in 2010 before the military dispersed them.

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Messrs. Abhisit and Suthep were in charge of a special command unit that ordered the security forces to quell the protesters, leading to the deaths and injuries, the attorney general's office said in a statement.

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"We have evidence that showed that Mr. Abhisit and Mr. Suthep ordered security forces to disperse the protesters and authorized the use of weapon and live ammunition," said spokesman Nanthasak Poonsuk of the attorney general's office.

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The attorney general's office said that although the deaths and injuries at the protests took place on different days, they were a "direct" consequence of the orders of both men. The statement didn't say how many counts of murder they were being charged with.

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Messrs. Abhisit and Suthep couldn't be reached to comment.

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The two men don't face immediate arrest and it wasn't immediately known when the two will be summoned to court. Messrs. Abhisit and Suthep are given legislative immunity from court proceedings while the Thai Parliament is in session. The next recess is in late November.

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Mr. Abhisit had said in the past that his party doesn't want to back the bill and allow Mr. Thaksin—the brother of current Prime Minister Yingluck Shinawatra—to return.

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"We don't want the amnesty bill to cover us," said Chavanond Intarakomalyasut, spokesman of the opposition Democrat Party. "We are willing to fight in court. We want to let the justice system run its course."

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The 2010 streets protests followed a period of turmoil after a military coup ousted Mr. Thaksin in 2006. Later, anti-Thaksin "yellow shirt" protesters campaigned against a pro-Thaksin government in 2008, blockading Bangkok's two international airports for a week.

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Mr. Abhisit took over as premier when the pro-Thaksin government collapsed, but was quickly faced with the red-shirt protesters, the grass-roots supporters of Mr. Thaksin who said Mr. Abhisit's rise to office was thanks to the backing of the people behind the coup, an accusation that Mr. Abhisit denied.

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The red-shirt protesters held rallies in downtown Bangkok and demanded that Mr. Abhisit call for a new election.

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After nine weeks, Mr. Abhisit ordered a crackdown on the protest, leading to one of the bloodiest clashes in years between the security forces and protesters that further polarized the politically divided Southeast Asian country.

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Mr. Abhisit's Democrat Party was defeated in elections in 2011 by Ms. Yingluck.

Supporters of the amnesty bill say it is necessary to heal a country prone to political unrest.

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The bill, as it stands, would clear all charges against all political parties involved in the conflict since the 2006 coup, including Mr. Thaksin, who was sentenced to two years in prison for a conflict of interest conviction, as well as Mr. Abhisit and the security forces. It diverted from the original version of the bill, which only granted amnesty to people accused of politically related crimes and not authorities or politicians.

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However, the path to pass the bill isn't easy. Already antigovernment groups said that if the Puea Thai-dominated House passes the bill, which is expected in November, it will call for mass rallies. The bill would then need to go through the Senate.

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The bill also upset some of the red-shirt groups and relatives of the slain protesters because it would also clear charges against Messrs. Abhisit and Suthep and military personnel whom many view as responsible for the crackdown.

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Democrat Party lawmaker Thavorn Senniem criticized the indictments, saying that the two political leaders were acting under the authority given to them by the state of emergency, which grants officials immunity from prosecution from actions under its provisions.

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A Thai court has ruled that some people—including protesters, a photographer and a taxi driver—in the 2010 rally period were killed by bullets fired by Thai soldiers, or fired from the direction of security forces. In August, an inquest by a Thai criminal court found that six unarmed people were killed at a Buddhist temple during the military crackdown by bullets fired by Thai soldiers.

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-- Wilawan Watcharasakwet contributed to this article.

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