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," he told US broadcaster ABC News.

He added that Ukraine could push Russian President Vladimir Putin to end the conflict, but only if Kyiv was coming from a "strong position" - once again calling on his Western allies to strengthen the Ukrainian army.

The Ukrainian president is in the US this week to speak at the United Nations General Assembly and to present what he has called a "victory plan" to his Western allies, including US President Joe Biden.

In a statement ahead of the visit, Zelensky said the plan included further weapons donations, diplomatic efforts to force Russia to agree to peace, and holding Moscow accountable for its full-scale invasion in 2022.

In his interview with ABC News, Zelensky said his victory plan was not about negotiating with Russia, but rather it was "a bridge to a diplomatic way out, to stop the war".

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 for some time been asking Western countries to allow Ukraine to ease restrictions on the use of long-range missiles which could be used to strike deep into Russia. 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 would 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.

An incursion by Ukrainian troops into Russia's Kursk region in August failed to ease the pressure put by Moscow on eastern Ukraine.

Several regions continue to see daily casualties and widespread damage to Ukraine's energy infrastructure. There are concerns Russia could seize more key towns in the east of the country.

In a daytime attack on Tuesday, Russia hit a high-rise apartment block in Ukraine's northeastern city of Kharkiv.

At least three people died and 15 were injured in the attack, which local authorities said was carried out with glide bombs.

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 others 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 front line 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 the eastern region of 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."