Washington: Ukrainian President Volodymyr Zelenskyy warned that the Kremlin would become a target and Russian officials should check for bomb shelters if Moscow does not stop its invasion of his country, Axios reported Thursday.

"They have to know where the bomb shelters are," Zelenskyy told Axios in an interview. "They need it. If they do not stop the war, they will need it in any case."

Russia said Wednesday it would press on with its military offensive in Ukraine, and rejected US President Donald Trump's claim that Kyiv's army could retake territory seized by Russian forces.

The Kremlin also pushed back at Trump's characterisation of Russia as a "paper tiger", a day after the US leader dismissed Russia's army and said he could see Ukraine winning back every inch of land captured by Russia's forces.

Trump's remarks, which followed talks with Ukrainian President Volodymyr Zelensky at the United Nations, were a major pivot in his stance on the three-and-a-half-year conflict, which he had at one point boasted he could end in hours.

In Moscow, Russians who spoke to AFP brushed off Trump's comments.

"America and Ukraine as a whole have absolutely no chance of defeating Russia," said 20-year-old university student Stepan Lastochkin.

"His words mean nothing to our people now."

The Kremlin said earlier it would "achieve the goals" of its offensive.

"We are doing this for both the present and the future of our country. For many generations to come. Therefore, we have no alternative," Kremlin spokesman Dmitry Peskov said in a radio interview.