BANGKOK, Thailand -- Thai police said Saturday that they have arrested a key anti-government protest leader and charged him with offences including insurrection, risking further political confrontations even though a court freed him on bail hours later.

Immigration police arrested Sakhontee Phattiyagul Friday night at Bangkok's international airport upon his return from a trip to the U.S., said Department of Special Investigation Director-General Tharit Pengdit.

Sakhontee is a leader of the People's Democratic Reform Committee, which has been staging anti-government demonstrations in Thailand's capital since November. The group wants Prime Minister Yingluck Shinawatra to step down and disrupted a general election held in February. It insists that an interim unelected government be appointed to implement measures against corruption and money politics.

Sakhontee was arrested on multiple charges, including insurrection, Tharit said. Thai media reported that a court on Saturday released him on 600,000 baht ($18,600) bail.

The protests have engendered an atmosphere of violence in Bangkok, where a pro-government activist was shot dead Wednesday by unidentified gunmen, and grenades were fired at a newspaper headquarters and a court on Thursday night, also by unknown attackers. There are fears the tempo of violence may increase as legal challenges to Yingluck's position, initiated by her political foes, come close to fruition over the next month.

More than 20 people have been killed and over 700 hurt since November in the current round of political confrontations.

Police have been frustrated in their attempts to arrest protest leaders, thwarted by courts quickly granting bail to protest leaders and legal rulings calling the demonstrations allowable under the constitution, even though many have turned violent.

The judiciary is seen as part of the Thai establishment, which is hostile to Yingluck's government.

Thailand has been plagued by political strife since a 2006 military coup ousted then-Prime Minister Thaksin Shinawatra, Yingluck's brother, after demonstrators accused him of corruption, abuse of power and disrespect for King Bhumibol Adulyadej.

Since the coup, Thaksin's opponents and supporters have contended for power, staging sometimes-violent street demonstrations. Thaksin lives overseas in self-imposed exile to escape a 2008 corruption conviction.

Thaksin's supporters believe the country's elite feel their privileges are threatened by his popularity, especially among rural and underprivileged citizens who benefited from his populist programs.