US President Donald Trump has said he is ready to impose tougher sanctions on Russia, but only if Nato countries meet certain conditions which include stopping buying Russian oil.

In a post on his Truth Social platform, he said he was "ready to do major sanctions on Russia" once Nato nations had "agreed, and started, to do the same thing".

Trump has repeatedly threatened tougher measures against Moscow, but has so far failed to take any action when the Kremlin ignored his deadlines and threats of sanctions.

He described the purchases of Russian oil as "shocking" and also suggested that Nato place 50 to 100% tariffs on China, claiming it would weaken its "strong control" over Russia.

In what he called a letter to Nato nations, Trump said: "I am ready to 'go' when you are. Just say when?"

He added "the purchase of Russian oil, by some, has been shocking! It greatly weakens your negotiating position, and bargaining power, over Russia".

Trump also claimed the halt on Russian energy purchases, combined with heavy tariffs on China "to be fully withdrawn" after the war, would be of "great help" in ending the conflict.

Europe's reliance on Russian energy has fallen dramatically since the start of Moscow's full-scale invasion of Ukraine.

In 2022, the EU got about 45% of its gas from Russia. That is expected to fall to about 13% this year, though Trump's words suggest he feels that figure is not enough.

The US president's message came during heightened tensions between Nato allies and Russia after more than a dozen Russian drones entered Polish airspace on Wednesday.

Warsaw said the incursion was deliberate, but Moscow downplayed the incident and said it had "no plans to target" facilities in Poland.

Denmark, France and Germany have joined a new Nato mission to bolster the alliance's eastern flank, and will move military assets eastwards.

Last week, Ukrainian President Volodymyr Zelensky also made a demand to European nations over the purchase of Russian oil and gas.

In an interview with ABC News, he said: "We have to stop [buying] any kind of energy from Russia, and by the way, anything, any deals with Russia. We can't have any deals if we want to stop them."

Since 2022, European nations have spent around €210bn (£182bn) on Russian oil and gas, according to the think tank the Centre for Research on Energy and Clean Air, much of which will have funded the invasion of Ukraine.

The EU has previously committed to phasing out the purchases by 2028. The US want that to happen faster - partly by buying supplies from them instead.

Trump's message was to Nato, not the EU, therefore including nations such as Turkey, a major buyer of Russian oil and a country that has maintained closer relations with Moscow that any other member of the alliance.

Persuading Ankara to cut off Russian supplies may be a far harder task.

Trump's most recent threat of tougher sanctions on Russia came earlier in September after the Kremlin's heaviest bombardment on Ukraine since the war began.

Asked by reporters if he was prepared to move to the "second phase" of punishing Moscow, Trump replied: "Yeah, I am," though gave no details.

The US previously placed tariffs of 50% on goods from India - which included a 25% penalty for transactions with Russia that are a key source of funds for the war in Ukraine.