Thailand's army has denied supplying rice to units of Myanmar's armed forces and said on Saturday any food being sent over the border was part of normal trade.
Myanmar's military is facing international condemnation over a Feb. 1 coup and bloody crackdowns on protests against military rule in which nearly 250 people have been killed.
Thailand has voiced concern over the bloodshed.
Direct Thai assistance to the Myanmar military would likely draw criticism from supporters of the ousted government that was led by Aung San Suu Kyi. The Nobel peace laureate has been detained in Myanmar since the coup.
Thai media reported that the Thai army had supplied 700 sacks of rice to Myanmar army units on Myanmar's eastern border, citing an unidentified security official as saying it was on the orders of the Thai government.
"The Thai army is not supplying the Myanmar army and there has been no contact from the Myanmar army requesting help or demanding any assistance from us because they have their own honour," Major General Amnat Srimak, commander of the Naresuan Force, said in a statement.
"If there is anything, I think there is regular commerce at normal border crossings," Amnat said. "We are not blocking this if the conduct is not against the law and follows customs procedures."
A Thai government spokesman did not immediately respond to a Reuters request for comment. Myanmar's army did not answer calls seeking comment.
Thai media said the Myanmar army units being supplied near the border had been cut off by forces of the Karen National Union (KNU), an ethnic minority insurgent group that agreed to a ceasefire with the Myanmar government in 2012.
A KNU spokesman did not respond to a request for comment. The KNU has thrown its support behind Myanmar's democracy movement and condemned the military's coup and crackdown.
The Myanmar junta has defended its coup saying a Nov. 8 election won by Suu Kyi's National League for Democracy was fraudulent and its claims were ignored by the electoral commission. It has promised a new election but has not set a date.
Thai media showed pictures of what appeared to be bags of rice being loaded into trucks at the border. Pictures seen by Reuters showed men, some in camouflage uniform, crossing into Thailand and having their temperatures checked.
Border trade between Thailand and Myanmar has been severely restricted since the outbreak of the coronavirus pandemic. Residents told a Reuters reporter the crossing shown in the pictures was not a normal trade route.