U.S. officials have shifted emphasis this week from speaking mainly about helping Ukraine defend itself to bolder talk of a Ukrainian victory delivering a blow to Russia’s ability to threaten its neighbours.

They have approved shipments of hundreds of millions of dollars in arms, including artillery and drones they held back from sending in earlier phases of the war.

“Nations from around the world stand united in our resolve to support Ukraine in its fight against Russia’s imperial aggression,” Defence Secretary Lloyd Austin said, welcoming officials from more than 40 countries to Ramstein Air Base in Germany, headquarters of U.S. air power in Europe. “Ukraine clearly believes that it can win, and so does everyone here.”

In a marked escalation of Russian rhetoric, Foreign Minister Sergei Lavrov was asked on state TV about the prospect of World War Three and whether the current situation was comparable to the 1962 Cuban Missile Crisis that nearly caused nuclear war.

“The danger is serious, real. And we must not underestimate it,” Lavrov said, according to the ministry’s transcript of the interview. “NATO, in essence, is engaged in a war with Russia through a proxy and is arming that proxy. War means war.”

Chairman of the U.S. Joint Chiefs of Staff Mark Milley, flying to Tuesday’s meeting, told reporters the next several weeks in Ukraine would be “very, very critical”.

“They need continued support in order to be successful on the battlefield. And that’s really the purpose of this conference.”

The aim would be to coordinate aid that includes heavy weapons such as howitzer artillery, as well as killer drones and ammunition, General Milley said.

Austin, who visited Kyiv along with U.S. Secretary of State Antony Blinken on Sunday, had said on Monday: “We want to see Russia weakened to the degree that it can’t do the kinds of things that it has done in invading Ukraine.”

‘BRAVADO’

U.N. Secretary-General Antonio Guterres visited Moscow on a peace mission, although Kyiv and Western countries said they doubted he could achieve much.

“We are extremely interested in finding ways in order to create the conditions for effective dialogue, create the conditions for a ceasefire as soon as possible, create the conditions for a peaceful solution”, Guterres said at a meeting with Lavrov, ahead of a meeting with President Vladimir Putin.

Ukraine’ Foreign Minister Dmytro Kuleba said while a diplomatic breakthrough was unlikely, there was hope Guterres could help the humanitarian situation, esepecially around Mariupol, where Ukraine says hundreds of civilians are trapped with the city’s last defenders inside a blockaded steel works.

“I don’t think (the) Secretary General will be able to end the war. But there is one crucially important path that he can implement: It’s to arrange a green corridor for defenders and civilians blocked by Russia in Mariupol.”

Kyiv and its allies played down Lavrov’s remarks about nuclear war. Russia had lost its “last hope to scare the world off supporting Ukraine,” Kuleba tweeted after Lavrov’s interview. “This only means Moscow senses defeat.”

Pentagon spokesman John Kirby decried what he called Lavrov’s “escalatory rhetoric”.

“It’s obviously unhelpful, not constructive, and certainly is not indicative of what a responsible (world power) ought to be doing in the public sphere,” he said. “A nuclear war cannot be won and it shouldn’t be fought. There’s no reason for the current conflict in Ukraine to get to that level at all.”

MOLDOVA

To the west of Ukraine, there were fears unrest could spread to Moldova, where Russian troops have occupied a separatist region along the Ukrainian border, Transdniestria, since the 1990s. Two radio transmitters were destroyed by explosions early on Tuesday, following other blasts in Transdniestria on Monday.

The separatist authorities said they were raising their terrorism threat level to red, while the Kremlin said it was concerned. Moldova’s pro-Western President Maia Sandu convened her security officials in the capital Chisinau.

Sandu’s government expressed alarm last week after a top Russian general said Moscow aims to seize a path through Ukraine to Transdniestria, where he said Russian speakers needed protection from oppression. Moldova, an ex-Soviet state, has close cultural and linguistic ties to NATO member Romania.

Russia’s two-month-old invasion of Ukraine has left thousands dead or injured, reduced towns and cities to rubble, and forced more than 5 million people to flee abroad.

Moscow calls its actions a “special operation” to disarm Ukraine and protect it from fascists. Ukraine and the West call this a false pretext for an unprovoked war of aggression.

Russia was forced to pull its huge invasion force back from the outskirts of Kyiv last month, but has since announced new war aims to focus mainly on the east, sending more troops there for an assault on two provinces where it backs separatists.

Ukraine’s general staff said on Tuesday Russia’s offensive continued in the eastern Kharkiv region with Russian forces trying to advance towards a village called Zavody.

Russia is probably attempting to encircle heavily fortified Ukrainian positions in the country’s east, the British military said in an update on Tuesday, noting forces were trying to advance towards the cities of Sloviansk and Kramatorsk.

By Phil Stewart and Pavel Polityuk.

(Additional reporting by Reuters journalists; Writing by Peter Graff; Editing by Angus MacSwan)