The United States has announced new military aid for Ukraine and vowed to disrupt Russian ties with Iran, which a British envoy said involved Moscow seeking hundreds of ballistic missiles and offering unprecedented military support in return.

Tehran and Moscow have denied Western accusations that Russia is using Iranian drones to attack targets in Ukraine, where officials warned of a winter-long power deficit after repeated Russian attacks on its energy infrastructure.

Members of the public sit in a café without power in Lviv, Ukraine

Two senior Iranian officials and two Iranian diplomats told Reuters in October that Iran had promised to provide Russia with surface-to-surface missiles as well as more drones.

White House national security spokesman John Kirby told reporters Washington was very concerned about the "deepening and burgeoning defence partnership" between Iran and Russia, and would work to disrupt that relationship, including on drones.

Washington was sending a $275 million package of aid to Ukraine to strengthen air defences and defeat drones, he said.

Britain's UN Ambassador Barbara Woodward said Iran had sent hundreds of drones that Russia had used in Ukraine.

"Russia is now attempting to obtain more weapons, including hundreds of ballistic missiles," she told reporters.

"In return, Russia is offering Iran an unprecedented level of military and technical support."

The Iranian and Russian missions to the United Nations did not immediately respond to requests for comment.

Russian President Vladimir Putin earlier said Moscow would probably do a deal over Ukraine one day but that Russia's near-total loss of trust in the West would make an eventual settlement, which he did not elaborate on, much harder to reach.

Russia has clamped down on dissent since it invaded Ukraine in February, and a Moscow court today sentenced opposition politician Ilya Yashin to eight-and-a-half years in prison on charges of spreading "false information" about the army.

Ilya Yashin urged supporters to continue opposing the war

Yashin had discussed in a YouTube video evidence uncovered by Western journalists of Russian war crimes in Ukraine.

Moscow denies committing war crimes.

In a post on his Telegram channel, Yashin urged supporters to continue opposing the war.

The fiercest recent fighting has been near the eastern towns of Bakhmut and Avdiivka, the Donetsk region's governor Pavlo Kyrylenko said earlies, adding that five civilians were killed and two wounded in Ukrainian-controlled parts of Donetsk.

"The entire front line is being shelled," he said.

In an evening address, President Volodymyr Zelensky said the situation on the Donbas front remained very difficult, but Kyiv's forces were repelling Russian attacks and inflicting significant losses.

Reuters was not able to verify battlefield reports.

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'The question of trust'

Vladimir Putin

Vladimir Putin earlier repeated an accusation that the West was "exploiting" Ukraine and using its people as "cannon fodder" in a conflict with Russia, and said the West's desire to maintain its global dominance was increasing risks.

"They deliberately multiply chaos and aggravate the international situation," Mr Putin said in a video message to a summit of defence ministers from the Shanghai Cooperation Organisation and a group of ex-Soviet states.

He later specifically criticised France and Germany, which in 2014 and 2015 brokered ceasefire accords between Kyiv and Russian-backed separatists in eastern Ukraine, saying they had betrayed Moscow by supplying Ukraine with weapons.

"The question of trust arises. And trust of course is almost at zero... But nevertheless, in the final analysis we have to come to agreements. I have already said many times that we are ready for these agreements," Mr Putin said.

Mr Putin, who was speaking in the Kyrgyz capital Bishkek, also said Russia - the world's biggest exporter of energy - might cut its oil production and would refuse to sell oil to any country that imposed the West's "stupid" price cap on Russian oil.

The Group of Seven major powers, the European Union and Australia last week agreed a $60 per barrel price cap on Russian seaborne crude oil.

Prisoner swap

A plane carrying Brittney Griner landed in the United States earlier today (File pic)

Yet in a reminder that, despite the hostilities, Russia maintains lines of communication with the West, Moscow yesterday freed US basketball player Brittney Griner in return for the release of Russian arms dealer Viktor Bout.

A plane carrying Ms Griner landed in the United States earlier, nearly ten months after she was detained in Russia on drug charges, while television images showed Bout being hugged by his mother and wife after landing in Moscow.

Vladimir Putin said further prisoner swaps were possible and the White House said it would work to gain the release of Paul Whelan, a US Marine Corps veteran convicted of espionage in 2020 in a trial that US diplomats said was unfair and opaque.

The Kremlin said the prisoner swap should not be seen as a step towards improving bilateral ties between Moscow and Washington, while the White House said it would not change its commitment to the people of Ukraine.

Workers install construction elements of a bridge donated to Ukraine by France to restore transport connections in the Chernihiv region

Separately, Russian and US diplomats met in Istanbul to discuss a number of technical issues in their vexed relationship, both sides confirmed, though the Ukraine war was not part of their talks.

Russia has targeted Ukraine's energy infrastructure in recent weeks, leaving millions without heating and electricity.

The head of Ukraine's state energy company Ukrenergo, Volodymyr Kudrytskyi, said more than 1,000 missiles and drones had hit the country's energy systems since October.

Ukraine's atomic power agency has accused Russian forces of abducting two senior Ukrainian staff at the Russian-occupied Zaporizhzhia nuclear power station and detaining a third.