According to one US general, Russia's foreign minister accused Nato of waging a proxy war in Ukraine by providing military assistance, as defense ministers convened in Germany for US-hosted discussions on assisting Ukraine during a "critical" few weeks.

Sergei Lavrov told Russian state media: "Nato is essentially fighting a proxy war with Russia and arming that proxy." War is synonymous with war."

He also warned that the possibility of nuclear conflict had increased to "considerable" levels - a warning that Ukraine's foreign minister, Dmytro Kuleba, said showed Moscow had exhausted its "last hope of scaring the world away from supporting Ukraine."

When asked about the critical nature of averting a third global war, Lavrov stated: "I would not want to inflate those risks artificially." That would be ideal for many. The risk is grave and present. And it is not to be underestimated."

Western officials have expressed alarm about Moscow's growing reliance on its nuclear weapons. Its conventional forces have struggled in Ukraine, impeded by stiff resistance and internal logistical and technological difficulties.

The US discussions, sponsored by US Defense Secretary Lloyd Austin in Germany, are anticipated to bring together representatives from more than 40 countries and the UN Secretary-General, Jens Stoltenberg, at the Ramstein airbase south of Frankfurt. General Mark Milley, chairman of the Joint Chiefs of Staff of the United States, said a primary objective of the meeting was to coordinate increasing security assistance to Kyiv that included heavy equipment such as howitzers and well-armed drones and ammunition.

"The next few weeks will be critical," Milley stated. "They require ongoing assistance to be successful on the battlefield. That, in fact, is the objective of this conference."

After he visited Ukraine, Austin stated, "They [Ukraine] can win if they have the proper equipment and support."

According to the US sources speaking on anonymity, Russia will now depend mainly on artillery strikes to pound Ukrainian positions. At the same time, Moscow advances ground forces from numerous angles to encircle and destroy a sizable portion of Ukraine's military.

However, the US estimates that many Russian units are depleted, with some operating with troop losses of up to 30% - a level deemed too high by the US military to continue fighting, officials say.

Ben Wallace, the British defense secretary, told parliament on Monday that approximately 15,000 Russian troops had been killed or captured since the invasion began on 24 February; 2,000 Russian armored vehicles, including 530 tanks, had been destroyed or captured; and more than 60 Russian helicopters and fighter jets had been lost.

Ukraine's foreign minister asked Guterres on Monday to encourage Russia for an evacuation of the beleaguered Mariupol port and criticized Guterres' intention to visit Moscow first on Tuesday before heading to Kyiv.

"Many other foreign officials were trapped in Moscow and played around solely to demonstrate Russia's diplomacy's supremacy and how great they are at dictating how the world should behave," Kuleba said.

Guterres "should concentrate on a single issue: Mariupol evacuation," Kuleba said, referring to the southern port city where 100,000 people are stranded. At the same time, Ukrainian fighters holed up in a steelwork battle against Russian soldiers. "This is something that the UN is capable of accomplishing. And I hope that if he [Guterres] exhibits political will, character, and integrity, we can take a step ahead."