US President Donald Trump has set a new tighter deadline for Russia to agree to a ceasefire with Ukraine.

On July 14, Trump called on Russian President Vladimir Putin to agree to a deal within 50 days. He threatened severe tariffs if Moscow does not act within the timeframe that ends in early September.

Speaking to reporters during his visit to Scotland on Monday, Trump expressed disappointment with Putin again and said he is going to reduce the 50 days to a shorter period.

He said: "I'm going to make a new deadline of about 10 or 12 days from today. There is no reason to waiting."

He added, "I want to be generous but we just don't see any progress being made."

Regarding possible responses to Russia's failure to act by the new deadline, Trump said, "It would be sanctions and maybe tariffs, secondary tariffs."

He suggested that the secondary levies could hit imports to the US from countries buying Russian products.

Trump also said he is not so interested in talking with Putin anymore. He said, "We have such nice conversations, such respectful and nice conversations and then people die the following night with a missile going into a town."

In a social media post on Monday, Ukrainian President Volodymyr Zelenskyy welcomed Trump's decision to move up the date.

Zelenskyy said Trump's "clear stance and expressed determination" is "right on time, when a lot can change through strength for real peace."

He thanked the US president and said Ukraine remains committed to peace and will work tirelessly with the US.

On the same day, former Russian President Dmitry Medvedev wrote on social media that "Trump's playing the ultimatum game with Russia."

Medvedev, who currently serves as deputy chair of Russia's Security Council, also said: "Each new ultimatum is a threat and a step towards war. Not between Russia and Ukraine, but with his own country."