BANGKOK - Thai police said on Sunday (March 19) they had uncovered a plot to assassinate the country's prime minister after seizing a weapons cache belonging to a fugitive anti-junta activist.

It is the latest discovery of a weapons stockpile belonging to a member of the red shirt movement, a political group loyal to exiled Prime Minister Thaksin Shinawatra.

But red shirt leader Wuthipong Kochathamakun denied the allegation, saying the raid on his house was a government set-up.

Police on Saturday found four M-16 rifles, one M79 grenade launcher, and 13 guns, plus 5,000 rounds of ammunition, three red shirt banners and other material deemed to violate the lese majeste law in Wuthipong's house in Pathum Thani.

Police also arrested nine men in connection with the arms seizure, saying they had clear evidence the suspects and their extended network were aiming to cause unrest, reported Reuters.

"We found a rifle with a scope. We guarantee that this is not to shoot at birds but was going to be used to assassinate the leader of the country," National Police Chief Jakthip Chaijinda told reporters on Sunday, referring to Prime Minister Prayut Chan-o-cha.

Prayut, then the army chief, overthrew the government of Thaksin's sister Yingluck in the 2014 coup.

His junta has discovered dozens of weapon caches belonging to groups they said were loyal to the Shinawatra clan. The junta said the stockpiles showed there were groups trying to create instability and justified their seizure of power.

Police chief Jakthip said the suspects arrested also had plans to assassinate deputy prime minister Prawit Wongsuwan, reported The Nation newspaper.

Jakthip presented no other evidence of an assassination plot, but said Wuthipong and his network had always opposed the junta and the group had predicted on social media that the prime minister would be killed.

Police said the group was planning an ambush if officials had continued their operations against a influential nearby Buddhist temple, which is seen as having close ties to Thaksin.

Thai police ended their search of the Dhammakaya temple earlier this month after laying siege to it for more than three weeks without finding the former abbot, who is wanted for suspected money laundering.

Wuthipong, alias Ko Tee, is wanted in Thailand on a lese majeste charge. A warrant was issued for his arrest in April 2014 and he has been on the run since.

He defended himself on Sunday through a YouTube-based radio programme, suggesting that the raid was a government set-up, reported The Nation.

Weng Tojirakarn, co-leader of the United Front for Democracy against Dictatorship (UDD) which is a red shirt umbrella group, also asked why officers only now decided to search the house, three years after Wuthipong faced charges.

He said authorities were attempting to link the discovery of the weapons with the Dhammakaya temple and the UDD without evidence, in order to frame the red shirts as an armed group. Weng also insisted that Wuthipong had nothing to do with the UDD movement, reported Bangkok Post.

Government spokesman Sansern Kaewkamnerd denied that the raid was a set-up.