No trade takes place between Thailand and North Korea, Prime Minister Prayut Chan-o-cha said on Tuesday, ahead of an expected visit by a US envoy seeking to step up pressure on North Korea over its weapons programmes.
The United States has been urging Southeast Asian countries to do more to cut funding streams for North Korea as tension mounts over its development of nuclear weapons and missiles to carry them as far as the United States.
"Thailand guarantees ... that we have abided by the United Nations resolutions," Gen Prayut Chan-o-cha told reporters at his official Government House offices.
"There have been reports about North Korean boats in our waters ... I prohibited them a long time ago. There is no trade ... there is no commerce," he said.
Joseph Yun, the US special representative for North Korea policy, is due in Bangkok this week to discuss stepping up pressure on North Korea which has been pressing ahead with its weapons tests in defiance of UN resolutions and sanctions.
During a visit to Bangkok in August, US Secretary of State Rex Tillerson pressed Thailand, the United States' oldest ally in Asia, for more action on North Korea.
At the time, the United States said it believed North Korean companies were active in Thailand and said it was encouraging the Thailand to close them.
Following Tillerson's visit, Thailand's foreign ministry said trade with North Korea had dropped by as much as 94% over the previous year. It did not give any more detail.
North Korea tested its most powerful intercontinental ballistic missile late last month.
The UN Security Council is due to hold a ministerial meeting on North Korea's nuclear and missiles programmes on Friday.