By Amy Sawitta Lefevre
NAKHON NAYOK, Thailand (Reuters) - The United States said on Monday its relationship with longtime ally Thailand was going through a "challenging" period as the two sides began a major military exercise, scaled down over Washington's concerns about the junta leadership.
Cobra Gold, the largest military exercise in the Asia-Pacific, has been held annually in Thailand for more than three decades, but the United States scaled the drill back this year after sanctioning Bangkok for last year's coup.
"We can't deny that this period is a challenging one and has necessitated a modified Cobra Gold as Thailand manages its return to democracy," U.S. charge d'affaires Patrick Murphy Murphy said in a speech at the opening ceremony for Cobra Gold at a military academy in Nakhon Nayok, east of Bangkok.
The Thai army took control last May saying it needed to restore order after months of political unrest that killed nearly 30 people. The United States responded by freezing $4.7 million (3.1 million pounds) of security-related aid and cancelling some security cooperation.
Comments by a visiting U.S. envoy last month, including that Thailand immediately lift martial law which has been in place since May, further strained ties. Senior Thai ministers responded by telling the U.S. not to meddle in Thailand's political affairs.
Last week Prime Minister Prayuth Chan-ocha, a former army chief, said a general election would take place in 2016 but stopped short of giving a specific date. His military government has said martial law will remain in place indefinitely.
Washington has sent 3,600 troops for this year's exercise, down from 4,300 last year, the U.S. Embassy in Bangkok said in an e-mailed statement.
The exercise comes as Thailand seeks to counterbalance its ties with Washington by cozying up to regional superpower China which says it supports the Thai military government.
Ian Storey, senior fellow at the Institute of Southeast Asian Studies in Singapore specializing in Asian security issues, said that cancelling the exercise could have had major security implications in the region.
"Cancelling them would have created an opportunity for Beijing to strengthen its strategic ties to Bangkok, and that is clearly something that is not in Washington's interests in the context of U.S.- China competition in Southeast Asia," he said.
Last year's coup was the latest chapter in over a decade of political jostling in Thailand including sometimes violent struggles between the Bangkok-based middle classes and elite, who revile former Prime Minister Thaksin Shinawatra and his family and see them as a threat to the conservative political status quo, and his mostly rural supporters in the north and northeast.