The UK has called for an urgent meeting of the UN security council to update council members on the investigation into the nerve agent attack in Salisbury, the Foreign Office said, as Theresa May prepared to set out a range of reprisals against the Russian state.

The measures, which are likely to include the expulsion of diplomats, will be put to parliament in a statement by the prime minister on Wednesday, after a midnight deadline passed for the Kremlin to explain why a former spy was poisoned by a Russian-manufactured nerve agent.

Russia, which is a permanent member of the UN security council, said there would be retaliation against any fresh measures and that the UK had so far offered only “baseless accusations which are not backed up by any evidence”.

A spokesman for Vladimir Putin said Russia “rejects the language of ultimatums”, while a foreign ministry spokeswoman said Britain must not try to threaten Moscow, pointing to Putin’s recent speech in which he presented a range of new nuclear weapons.

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The prime minister will lay out her proposals for reprisals in the House of Commons on Wednesday, after a day of diplomacy during which she sought support from the US president, Donald Trump, as well as Nato and EU allies including Germany’s chancellor, Angela Merkel.

May chaired the council, which is attended by a select group of cabinet ministers, including the Cabinet Office minister, David Lidington, the chancellor, Philip Hammond, the foreign secretary, Boris Johnson, the home secretary, Amber Rudd, and the defence secretary, Gavin Williamson, as well as May’s most senior security adviser, Mark Sedwill.

Downing Street said Trump had given his full backing to the UK in confronting Russia over the poisoning of the former double agent Sergei Skripal, after a chaotic 12 hours during which the president fired his secretary of state, Rex Tillerson.