On Monday President Donald Trump on Truth Social said that he did not believe that China and Russia were helping Iran "at all," adding that Moscow and Beijing had "too much to lose" if they enabled Tehran.
Trump said on Truth Social that he had seen comments from his critics and opponents that China and Russia were helping Iran.
"If they are, it's at a very low level, but I don't believe they are at all. They have too much to lose, and we would know about it, and know about it very fast," Trump wrote.
In July, Trump said that he trusted China and Russia not to help Tehran in the Iran war, but warned that if they did get involved "it would be very bad for them."
The US-Iran war has entered into 8th month in October, since its started in Feb 28, after US Isarel strike Tehran, followed by Iran's retaliation on US bases in gulf countries. US-Israeli strikes on Iran and Israeli attacks on Lebanon have since killed thousands and displaced millions.
Earlier, Trump has described China and Russia as "neutral" countries during the Iran war.
However, Moscow and Beijing maintain close ties with Tehran. Both Russia and China have criticised the US action against Iran, maintaining Iran's right to protect sovereignty.
Russia has said the Iran war could lead to a nuclear arms race in the Middle East. Beijing has condemned Washington's attacks on Tehran as a brazen violation of Iran's sovereignty.
According to media reports after Xi-Trump meet last month in Washington, Trump asked Xi not to support Iran in war against US, and received assurances from China, US ambassador to China said at the time.
Trump's comment came amid reports that China had supplied Iran with shoulder-fired air-defense missile launchers and that Tehran had found ways to evade sanctions on its oil sales with Chinese help.
In September, Trump brushed aside a report that Iran acquired satellite images of a base in Jordan from Chinese entities before an attack that killed three US troops there in July.