Russia has threatened to wage war across Ukraine if the West delivers long-range weapons to Kyiv.

Sergei Lavrov, the foreign minister, said the geographical objectives of Moscow's "special military operation" are no longer limited to the eastern Donbas region.

He added that Kremlin forces will expand still further if the West delivers long-range weapons to Kyiv, RIA Novosti, a Russian state news agency reported.

President Vladimir Putin claimed the invasion was to demilitarise and "denazify" Ukraine but would focus on the "liberation of Donbas" after his forces failed to take the capital Kyiv.

It comes as Lloyd Austin, the US defence secretary, said that the United States will send four additional high mobility artillery rocket systems (HIMARS) to Ukraine.

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Syria has announced that it was severing ties with Ukraine in support of its close ally Russia, saying the move was a response to a similar move by Kyiv.

"The Syrian Arab Republic has decided to break diplomatic relations with Ukraine in conformity with the principle of reciprocity and in response to the decision of the Ukrainian government," a foreign ministry official, who was not identified, told the state news agency SANA.

Ukrainian President Volodymyr Zelensky already announced he was severing ties with Syria late last month after Syria recognised the Russian-backed breakaway republics of Donetsk and Luhansk in eastern Ukraine.

"There will no longer be relations between Ukraine and Syria," Mr Zelensky said at the time.

The breakaway states of Donetsk and Luhansk, whose independence Moscow recognised in February, are situated in the Donbas region at the centre of Russia's invasion of Ukraine which was launched on February 24.

Syria was the first country apart from Russia to recognise their independence.