US President Donald Trump said on Monday he intends to shorten the 50-day deadline he gave Russian President Vladimir Putin to reach a deal that ends the three-year war in Ukraine.

His announcement came as Russia fired an overnight barrage at Ukraine of more than 300 drones, four cruise missiles and three ballistic missiles, the Ukrainian air force said.

Trump said two weeks ago he would implement "severe tariffs" on Russia unless a peace deal is reached by early September, as he expressed exasperation with Putin over the bombardment of Ukrainian cities amid the Republican president's attempts to stop the fighting.

The US president said he would give Putin 10 to 12 days from Monday, meaning he wants peace efforts to make progress by Aug 7-9. The plan includes possible sanctions and secondary tariffs targeting Russia's trading partners.