Kyiv, Ukraine - Ukrainian President Volodymyr Zelensky said Saturday that Russia wanted to achieve a "stronger position" militarily before committing to any ceasefire in the war in Ukraine.

Russia earlier this week did not immediately agree to a 30-day ceasefire proposed by the US, as President Vladimir Putin raised questions about the initiative.

"They want a stronger position before the ceasefire," Zelensky said at a press conference in Kyiv.

"I think the delaying of the process is exactly because of what I said. They want to improve their situation on the battlefield," he added.

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The ceasefire proposal comes as Russia has the momentum in many areas of the front in Ukraine, three years into its invasion.

Moscow has also ousted Ukrainian troops from swathes of Russia's Kursk region, where Ukraine had led a shock offensive last summer.

Zelensky said that by not agreeing to the ceasefire, Putin was also going against Trump – who has made some friendly statements on Russia – and accused Moscow of trying to find ways not to end the war.

"Today, Putin is the one who doesn't agree with what Trump has proposed," Zelensky said.

The Ukrainian leader said a 30-day ceasefire would allow negotiations on a long-term peace, though he ruled out ceding any territory to Russia.

"The United States raised this issue at a meeting in Jeddah. They got the Ukrainian position," Zelensky said, referring to talks between US and Ukrainian teams in Saudi Arabia.

"Our position is that we do not recognize the occupied Ukrainian territories as Russian in any case," he repeated.

Zelensky said the issue of territories was complex and should be "resolved later, at the negotiating table."

Russia has occupied large parts of southern and eastern Ukraine, with Moscow claiming to have annexed four Ukrainian regions, despite not controlling them fully.