TAIPEI — Thailand's move to purchase Chinese submarines has exacerbated tensions with the US and poses a challenge to Washington's "pivot" to the Pacific.

The military junta, which declared a coup in May 2014 and created the National Council for Peace and Order, could turn to China for political and military support and cooperation, analysts said. The junta-led Cabinet approved the purchase of three Type 039A (Yuan) attack submarines in early July.

After the coup, the US reduced its presence at the annual Cobra Gold military exercises held with Thailand, and postponed further discussion on planning 2016 exercises.

There are fears in the region that US sanctions are pushing Thailand into China's political sphere, said Martin Sebastian, head of the Centre for Maritime Security and Diplomacy, Maritime Institute of Malaysia.

"The US is giving the junta the cold shoulder, apparent during the Cobra Gold Exercise," he said.

The sub decision will worsen the drift in Thai-US relations and frustrate the US' rebalance strategy, said Thitinan Pongsudhirak, director of the Institute of Security and International Studies at Bangkok's Chulalongkorn University.

"It is building into a kind of brinkmanship from Bangkok which will require the US to weigh its values and interests carefully," he said

US criticism might be the prime driver for the turn toward China, Pongsudhirak said.

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"Evidently, Thailand's military government has found superpower support in Beijing, as China has embraced Thai generals in both coups in 2006 and 2014," he said. "Having China on its side is hugely important to the Thai military because it confers 'face' and international legitimacy while Western countries generally shunned and downgraded dealings with Thailand."

The new constitution drafted by the junta will no doubt cause more problems with the US, Sebastian said. Critics and activists are warning that the constitution includes anti-democratic provisions designed to prevent any group loyal to Thaksin Shinawatra, who served as prime minister from 2001 until the 2006 military coup, from returning to power.

"The current completed draft reportedly confirms these fears. Unelected individuals can become prime minister with parliamentary support, while most lawmakers would be appointed rather than elected. And parliament will also be elected via proportional representation, a system that would dilute the power of any large party and favor small parties and coalitions," he said. Such a system likely would draw the ire of the US, he said.

During the Cold War, the US and Thailand maintained a robust military exchange that evolved into the Cobra Gold exercises in 1982. Since the 1980s, the Thai Navy's procurement of ships ranged from across the globe, including China, Italy, Singapore, Scotland, Spain and the US. During the 1990s, China sold two Chinese Type-25T frigates and four Jianghu III-class guided missile frigates to Thailand, but both have been plagued with technical problems, including integration issues with third-party technologies.

Thailand procured a Spanish aircraft carrier in the 1990s but had difficulty with maintenance. Its nine AV-8 Harrier jump jet fighters are now inoperative and the carrier spends most of its time in dock, though occasionally it participates in regional disaster relief missions with a handful of helicopters, including a few Sikorsky Knighthawks and Seahawks.

The submarine selection surprised even Thai defense and security analysts in Thailand, Pongsudhirak said.

"Edging closer to China is understandable, even necessary, but buying submarines from the Chinese is something else much more alarming when other bidders such as Germany or Sweden seemed to make more sense."

The military junta has been unwilling to explain to the public why Thailand needs submarines and why they are being purchased from China, he said.

The submarine decision has taken the "geopolitical game into a new alarming level" for Bangkok, Pongsudhirak said. Purchasing submarines is a large and long-term commitment.

"It puts Thailand's eggs in the Chinese basket — perhaps too many eggs — not to mention logistical and practical issues such as interoperability," he said.

The selection of Chinese submarines and increased military exchanges with China demonstrates that Thailand will not be subject to further political bullying from the West.

Tim Huxley, executive director of the International Institute of Strategic Studies-Asia, Singapore, said the Thais are trying to show the US that its policy of punishing Thailand for last year's military coup and the continuing military dominance of the country's politics is not cost-free. He said it comes at a time when the US is trying to bolster its alliances and security partnerships in the region amid rising inter-state competition, while Thailand is demonstrating that it can improve its relations with China if it wants to.

From the Thai perspective, China is an increasingly important economic partner and there are no direct security-related conflicts between Bangkok and Beijing. Thailand, though, does place some value on Association of Southeast Asian Nations (ASEAN) cohesion and does object to China's behavior in the South China Sea and its impact on ASEAN partners, Huxley said.

"On its part, China sees Thailand as an important friend in Southeast Asia. However, the bilateral Sino-Thai relationship has developed gradually over several decades, and what we are seeing now is an uptick in a long-term trend rather than a dramatically new development," he said.

In the medium- to long-term, Huxley said, continued US emphasis on democracy in Thailand could push Bangkok even closer to Beijing in strategic terms. As for the submarine purchase, there are those who doubt that it will proceed, he said, as the Thai armed forces' reluctance to acquire Chinese equipment is well known — reflecting earlier disappointments — and that they have a general preference for US and other Western equipment.

The prospective submarine purchase may just be a tactic to worry the US and the West generally, he said.

"Buying Chinese submarines will exacerbate the drift in Thai-US relations and frustrate the US' rebalance strategy," Pongsudhirak said. Even prior to the 2006 coup, and between the 2006 and 2014 coups, when civilian governments were in charge, Thailand was gravitating more into China's strategic orbit in mainland Southeast Asia, he said.