[JURIST] AP is reporting that the Royal Thai Army [official website] has revoked the 1991 Thai constitution [PDF text; EN backgrounder] and declared martial law in a coup ousting Thai Prime Minister Thaksin Shinawatra [official website; BBC profile], who is in New York for the opening of the 61st session of the UN General Assembly. Earlier Tuesday, amid rumors of a coup and reports of army tanks surrounding government buildings, Thaksin sacked Army Commander-in-Chief Gen. Sonthi Boonyaratkalin [Sobaka profile] and declared a state of emergency [JURIST report] in Bangkok.

Sonthi, who became the first Muslim to serve as Army chief when he was named to the post in 2005, ordered all troops to report to report to their stations and a senior military officer has said that Thai military chiefs are working with King Bhumibol Adulyadej [official profile] to form an interim government. The military's initial announcement of the coup declared that a "Council of Administrative Reform" has taken power in Bangkok and surrounding provinces and named Bhumibol as head of state.

Tuesday's coup is the first in the country in 15 years, though there have been 17 coups in Thailand [JURIST news archive] since an absolute monarchy was abolished in 1932. New regimes have frequently drafted a new constitution after taking power.

Thaksin has been under intense pressure to resign for several months and last week said that he "may take a break" from politics [Xinhua report; JURIST report]. His Thai Rak Thai party [party website] called parliamentary elections in April, but the results were later annulled [JURIST report] by the nation's highest courts. Several members of the Election Commission of Thailand [official website, in Thai] have been convicted [JURIST report] for violating election laws in connection with arrangements for the April elections and the Thai Rak Thai party has been accused of election fraud [JURIST report], though Thaksin has denied those allegations [JURIST report]. New elections had been scheduled for November. AP has more. The Guardian has additional coverage.

3:08 PM ET – AP is reporting that a military spokesman has said that Sonthi will become acting prime minister.