Russia has warned that it will fire on western armaments shipments to Kyiv, raising the risk of a direct military confrontation between Moscow and Nato during the war in Ukraine.

Deputy foreign minister Sergei Ryabkov said on Saturday that “pumping up [Ukraine] with weapons from a whole range of countries” was “not just a dangerous move — it’s something that turns these convoys into legitimate military targets”, according to the Interfax news agency.

US president Joe Biden has rejected calls from Kyiv to establish a no-fly zone over Ukraine and said Nato will not be drawn into an all-out conflict with Russia or send troops to defend the country.

However, Ukraine’s western backers have pledged significant military aid to the country. The US has promised $6.5bn in defence spending, with Biden on Saturday authorising $200mn in new security assistance. The UK, meanwhile, has sent 3,615 NLAW anti-tank missiles and Javelin anti-tank weapons while Nordic states have sent more than 10,000 anti-tank weapons.

Russian forces continued their assault on Ukraine on Saturday with fierce fighting on the outskirts of Kyiv and reports of a strike on an airfield at Vasylkiv, south of the capital. Ukraine police said that an ammunition depot was damaged, shells detonated and a fire broke out.

“The airport is completely destroyed. An arsenal of weapons exploded,” said Natalia Balasynovych, Vasylkiv’s mayor.

A food distribution centre to the west of Kyiv was also hit by shelling.

Russia pressed on with its aerial bombardment of the besieged city of Mariupol and struck a mosque there, according to Ukrainian authorities. There was no immediate confirmation of casualties.

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There were street protests in Melitopol where Vladimir Putin’s forces have detained Ivan Fedorov, the city’s mayor.

Ukraine’s president Volodymyr Zelensky called upon world leaders to pressure Moscow to release him. “We appeal to all world leaders who speak to Moscow. France, Germany, Israel and others,” said Zelensky.

The Ukrainian president said Russian losses were “simply astounding”, claiming the destruction of more than 360 tanks, 1,205 armoured vehicles, “almost 60 planes [and] more than 80 helicopters”. His claims could not be independently verified.

He also called for face-to-face peace talks with his Russian counterpart to be held in Jerusalem, adding that Israeli prime minister Naftali Bennett was well positioned to act as a mediator.

The Russians can’t talk to us about the [dangers of the] third world war and also call us legitimate targets.”

German Chancellor Olaf Scholz and French President Emmanuel Macron held a “very frank and very difficult” joint phone call with Putin on Saturday in which they demanded he stop the war in Ukraine but found him determined to continue, according to senior officials.

The Kremlin said Putin claimed that Ukraine’s armed forces were “blatantly violating international law” through “extrajudicial reprisals against dissidents, taking civilians hostage and using them as human shields, [and] putting heavy armaments in civilian areas near hospitals, schools, kindergartens, and so on.”

A French official rejected the accusations as a “Russian lie” and countered that Moscow’s targeting of civilians and bombardment of cities constituted “the worst kind of violation of international humanitarian law” and could be considered war crimes. 

“It’s up to President Putin to stop this war and we are applying the maximum pressure on him,” the official said, calling the western sanctions already applied against Russia “historic”, likening them to the sanctions regimes imposed on North Korea, Syria and Iran and threatening more if the situation worsened.

Russia’s threat to western arms shipments was not raised in the call by either side, the official said, adding: “The Russians can’t talk to us about the [dangers of the] third world war and also call us legitimate targets.”

Putin said that Russian and Ukrainian representatives had continued to negotiate via video link after talks earlier this week.

The war is now in its third week and the west has stepped up sanctions. On Friday G7 nations said they would end normal trade relations with Moscow.

In the latest step against Russia’s oligarchs, Italian authorities seized a superyacht valued at $530mn owned by Andrey Melnichenko in the port of Trieste.

Ryabkov accused the US of further inflaming relations by leading the western sanctions effort. “It’s the US that has ramped up tensions to the maximum in international affairs. And that’s before we get to what they’re doing in practice by supporting the criminal Kyiv regime,” Ryabkov said.

He added that Russia and the US were in “constant contact” and Moscow was still open to a strategic dialogue with Washington on arms control.

Putin is demanding that Ukraine recognises its 2014 annexation of the Crimean peninsula and the independence of two separatist statelets in the Donbas region, commits to demilitarisation and declares neutrality in its constitution.

Ukraine has said it is open to making some concessions but has described Moscow’s stance as a demand for “capitulation”.