The United States Pacific Command (USPACOM) has postponed its preparatory meeting for the Cobra Gold 2016 military exercise, said a source in the Thai armed forces.
The first preparatory meeting between Thai and US military authorities for next year's Cobra Gold military drill usually takes place in April in Hawaii.
The second meeting, occurring later in the year, is held in Thailand. Both sides survey the areas for exercises and discuss details for the war games to be held in February.
But this year, USPACOM told Thai authorities they will delay the preparatory meeting and it is not known when it will be rescheduled.
Despite this setback, Thailand has greeted the nomination of an ambassador by President Barack Obama as a positive sign.
Mr Obama nominated a former US envoy for North Korea policy,
Glyn Davies, to be ambassador to Thailand, after a six-month period with no ambassador.
However, it is likely to be months or even longer before the US Senate agrees to review Mr Davies' appointment. For reasons that have nothing to do with Thailand, dozens of appointments as ambassador are pending action because of several Republican-Democratic Party disputes.
The Thai military is confident the postponement of the Cobra Gold preparations will not lead to a cancellation of the annual exercise, which is the largest joint military exercise in the region and started in 1982.
Cobra Gold 2016 is meant to be a "heavy year" focusing on field exercises such as anti-terrorism operations, rescue, evacuation and landing of troops, according to the source.
"The armed forces are adopting a wait-and-see approach. We hope the US will not cancel the Cobra Gold 2016. They [USPACOM] may wait for policy guidelines from the US government, or for the result of the assessment of Thai anti-human trafficking efforts," said the source.
Following the May 22 coup last year, the US army substantially scaled down its Cobra Gold numbers from more than 8,000 in previous years to 3,700 in 2015.
At the launch of this year's Cobra Gold, US charge d'affaires W Patrick Murphy asked the Thai government to return to democracy as soon as possible to restore full engagement between the two countries.
Meanwhile, an army source said the US is closely observing the relations between Thailand and China and Russia, most notably the increasing military ties between Bangkok and Beijing.
Deputy Prime Minister and Defence Minister Prawit Wongsuwon visited China from April 8 until Friday, his second trip since the interim government came to power. He took with him his full team, including defence chiefs from the army, navy and air force. Chinese authorities also paid a visit to Thailand in February.
The Thai delegation had planned to discuss an agreement to purchase weapons from China and forge closer collaboration in military exercises.
The White House announced the nomination of Mr Davies as ambassador on Monday. The Senate has to endorse Mr Davies' appointment.
Washington suspended military aid to Thailand after the coup last May. The military-dominated government has cracked down on dissent and political opponents, and it remains unclear when civilian rule will be restored.
Mr Davies served as the Obama administration's point man for the diplomatic response to North Korea's nuclear programme between 2012 and 2014. Prior to that, he was the US representative to the International Atomic Energy Agency in Vienna.
- Military pleased: Nomination shows solid relations
The previous US ambassador to Thailand, Kristie Kenney, vacated the post in November last year.
The Thai Foreign Ministry said the US proposed the name of Mr Davies to the ministry on Feb 20 and the cabinet endorsed the nomination on March 27.
Maj Gen Wirachon Sukhonthapatipak, a member of Prime Minister Prayut Chan-o-cha's senior staff, welcomed the nomination as a sign the Obama administration gives importance to Thai-US relations.
In his view, the belated nomination of a US ambassador to Thailand had been due to a lengthy procedure in selecting the right man for the job.
Although Washington has downgraded relations with other countries where disagreements occurred, this was not the case with Thailand, he insisted.
Maj Gen Wirachon said relations between the military of the two countries had only "diminished" slightly since the coup. The armed forces of both countries maintained their joint Cobra Gold training, although it may have decreased in size. Arms procurement deals have also not been affected, he said.