The US has urged its allies to move "heaven and earth" to keep Kyiv stocked with weapons – as Russian forces continue to rain fire on eastern and southern Ukraine.

For the second day in a row, explosions also rocked the separatist region of Trans-Dniester in neighbouring Moldova, knocking out two powerful radio antennas close to the Ukrainian border.

No-one claimed responsibility for the attacks, but Ukraine all but blamed Russia.

It came amid growing international fears the war was beginning to spill further over borders.

And in a separate, apparently defiant move, it seemed Ukraine had begun taking the fight to its aggressor’s door – with reports of explosions at a weapons dump at Belgorod, inside Russia.

Meanwhile, in Germany, US Defence Secretary Lloyd Austin convened a meeting of officials from about 40 countries at the American air base at Ramstein.

There, he urged delegates to leave "with a common and transparent understanding of Ukraine’s near-term security requirements because we’re going to keep moving heaven and earth so that we can meet them".

In a speech tonight British Foreign Secretary Liz Truss is expected to say the West must prepare for the "long haul" to ensure Russia’s defeat in Ukraine and call for allies to increase defence spending and supply tanks and warplanes to Kyiv.

Speaking at the Mansion House in the City of London she will say: "We cannot be complacent – the fate of Ukraine remains in the balance.

"And let’s be clear – if Putin succeeds there will be untold further misery across Europe and terrible consequences across the globe. We would never feel safe again."

Over in Chernobyl, the director-general of the International Atomic Energy Agency, says it was possible an accident could have occurred when Russian troops seized control of the site of the 1986 nuclear disaster during the early stages of the war in Ukraine.

Speaking at the plant on Tuesday, Rafael Mariano Grossi said as Russian troops took over in February on their way to the capital Kyiv, there became a "nuclear safety situation which was not normal, and could have developed into an accident".

The site is now back in Ukrainian hands but Russians continue to hold a working nuclear power plant in southern Ukraine – the Zaporizhzhia plant – where there was fighting nearby in early March which damaged the plant’s training facility.

Focus on Donbas

After unexpectedly fierce resistance by Ukrainian forces thwarted Russia’s attempt to take its capital, Moscow’s focus is now the capture of the Donbas, the mostly Russian-speaking industrial region in eastern Ukraine.

In response, Ukraine’s pleas for heavy weaponry have intensified, and Germany announced it would be sending tanks – better suited for the Donbas, than around the capital Kyiv where much of the earlier fighting took place.

In key developments:

  • US State Department diplomats have begun returning to Lviv in Western Ukraine
  • Russia will stop gas supplies to Poland and Bulgaria from Wednesday, it has been announced
  • Russia’s President Vladimir Putin tells UN Secretary-General António Guterres, he still hopes to negotiate a peaceful settlement with Ukraine
  • UK Prime Minister Boris Johnson dampened down claims Russia will use tactical nuclear weapons
  • Russia’s defence ministry has claimed Ukraine has lost control of the entire Kherson region

Earlier in the day, officials in Poland and Bulgaria said Russia had suspended natural gas deliveries to the two NATO countries, over their refusal to pay for its supplies in Russian roubles.

This led Ukraine to accuse Russia of blackmailing Europe over energy in an attempt to break its allies.

Staunch Kremlin opponent Poland is among the European countries seeking the toughest sanctions against Russia for invading its neighbour.

The potential effect of the cut-off was not immediately clear. Poland said it was well-prepared for such a move after working for years to reduce its reliance on Russian energy.

But, Bulgaria gets more than 90% of its gas from Russia, and officials said they were working to find other sources.

Back to work

Meanwhile, the US State Department said diplomats had begun returning to Ukraine by making day trips to temporary offices in the western city of Lviv from neighbouring Poland.

It said the first group of diplomats crossed the Polish-Ukrainian border and travelled to Lviv on Tuesday morning.

State Department spokesman Ned Price said the agency has accelerated its review of re-opening the US embassy in Kyiv, which was closed shortly before Russia invaded Ukraine on 24 February.

He said it was hoped operations at the embassy would resume as soon as possible depending on the security situation in the capital.

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