Ukrainian President Volodymyr Zelensky has said the war with Russia could end sooner than some people think.

"I think that we are closer to peace than we think. We just have to be very strong, very strong," he said.

Speaking to US broadcaster ABC News, Zelensky also said that the victory plan he will present to US President Joe Biden this week will require Ukraine's allies to "strengthen" the Ukrainian army.

Zelensky said the plan is not about negotiating with Russia, but rather it is "a bridge to a diplomatic way out, to stop the war".

He added that Ukraine can only push Russian President Vladimir Putin to end the conflict if Kyiv is coming from a "strong position".

On Tuesday, Kremlin spokesman Dmitry Peskov said Russia was being cautious about media reports of a Ukrainian plan and added that the conflict would only end when Russia's aims were achieved.

Zelensky has long asked Western countries to allow Ukraine to ease restrictions on the use of long-range missiles which could be used to strike deep into Russia and he is expected to do so again this week as he visits the US.

On Sunday, Biden said he had not yet decided whether to give Ukraine the green light. Zelensky said the US would need to lead the decision: "Everybody's looking up to [BIden], and we need this to defend ourselves," he told ABC.

Zelensky will speak at the UN General Assembly on Wednesday and is also due to meet US presidential candidates Donald Trump and Kamala Harris.

The president of the Czech Republic, Petr Pavel, told the New York Times that Ukraine will have to be "realistic" about its prospects of recovering the areas in the east of the country which Russia has managed to gain over the last 31 months of war.

He added that the most likely outcome of the war was that a part of Ukrainian territory would remain under Russian occupation for a number of years.

A defeat of either Ukraine or Russia "will simply not happen", Pavel told the Times, adding that the end of the conflict would be "somewhere in between".

Zelensky's US trip comes as Ukraine continues to come under sustained attack by Russia.

On Monday night, an attack on the eastern Ukrainian town of Poltava damaged infrastructure, while in the southern city of Zaporizhzhia one person died and six were wounded following "massive air strikes".

Russian troops have made serious advances in the east and are closing in on Vuhledar - a city on the southern part of the Donbas frontline that the Russians have been trying to seize since the beginning of their full-scale invasion.

Ukrainian military expert and retired colonel Kostyantyn Mashovets warned his fellow Ukrainians they had to be "psychologically prepared" for the loss of Selydove, Toretsk and Vuhledar in Donbas.

"I would love to be wrong," he wrote on Facebook.

"But from the information I have... this is a very likely scenario of events in the near future."