BANGKOK (Reuters) - A Thai court jailed a firebrand leader of the "red shirt" opposition group on Tuesday, ruling that he had violated bail conditions by using "harsh words against others" while talking politics on TV.

Jatuporn Prompan is a key leader of the red shirts loyal to ousted former Prime Minister Thaksin Shinawatra and his sister, former Prime Minister Yingluck Shinawatra, whose governments were ousted in military coups in 2006 and 2014 respectively.

Thailand has been ruled since May 2014 by a junta which has moved to suppress dissent and detained critics, many of them red shirt sympathizers.

Jatuporn, along with 18 others, was charged in 2010 with terrorism. A court granted him bail on the condition that he did not insult or defame others or stoke unrest.

On Tuesday, a Bangkok criminal court ordered Jatuporn's bail be revoked, while throwing out cases against four other leaders.

"The court sees from Jatuporn's recent behavior while expressing his opinion that he has used harsh words against others," a judge said.

"This violates the conditions previously set out by the court for bail."

Jatuporn was a leader during 2010 street protests in which red shirt supporters occupied a Bangkok shopping district for nearly two months, calling for then-Prime Minister Abhisit Vejjajiva to resign.

The protests ended in a bloody confrontation with the military in which more than 90 people were killed, most of them civilians.

Jatuporn was taken to the high-security Bangkok Remand Prison following the ruling.

Nattawut Saikua, another leader of the red shirt group, formally known as the United Front for Democracy against Dictatorship, told reporters the group would continue to express opinions on the government, but would be more careful.

"Although not a loss of life, it's a loss of freedom of speech for Jatuporn," said Nattawut.

Thailand has been broadly divided for more than a decade between opponents and supporters of Thaksin who lives in self-imposed exile in Dubai to avoid a 2008 jail sentence for corruption.

(Reporting by Aukkarapon Niyomyat; Writing by Patpicha Tanakasempipat; Editing by Amy Sawitta Lefevre and Nick Macfie)