Foreign Minister Surapong Tovichakchaikul said he was not aware of the rumoured plot to assassinate fugitive former premier Thaksin Shinawatra during his coming trip to Myanmar.
Mr Surapong said on Monday he had heard nothing about such a plot from the government of Myanmar.
Panthongtae Shinawatra, Thaksin's son, said in a message on his Facebook page on Sunday that he had information from Thai border authorities that weapons and ammunition seized near the border by Thai troops would have been used to attack a pagoda in Tachilek where his father and red-shirt supporters will attend a merit-making event.
Mr Panthongtae said he believed a group of Thais were behind the plot, which he claimed was the fifth attempt on his father's life. He said it involves the same group of people.
Democrat Party list MP Ong-Art Klampaiboon said Mr Panthongtae needed to be more careful when posting such a message about a rumoured assassination plot against his father. It was quite normal for Thai authorities to search for, and seize, weapons along the border.
On Sunday, Thai soldiers reportedly seized rifles, machine guns and other weapons, and more than 100,000 rounds of ammunition in Tak's Mae Sot district, near the Thai-Myanmar border.
Army sources said the weapons were found in a pickup truck without a licence plate and the driver was a Karen man.
The sources said the confiscated weapons were likely to be transported to the Border Guard Force (BGF) units in Karen state, Myanmar.
Thaksin will meet Myanmar President Thein Sein on Thursday when he visits Nay Pyi Taw as a part of his three-day trip to the neighbouring country.