- PM poised to unveil Russia response as deadline looms
- Moscow refuses to yield to ultimatum without seeing samples
- Trump tells May he stands "with the UK all the way" on Salisbury
- Merkel joins allies in supporting UK with "full solidarity" pledge
- Fresh terror probe as another Putin enemy dies in UK
Donald Trump has told Theresa May the US backs the UK "all the way" after blaming Russia for the poisoning of ex-spy Sergei Skripal and his daughter in Salisbury as the midnight deadline for Moscow to respond to the claim passed.
During a telephone conversation between the Prime Minister and US President, Trump agreed that Moscow must provide "unambiguous answers" as to how the Novichok nerve agent came to be used.
The Russian Embassy said hours before the deadline that the Kremlin "will not respond to London's ultimatum" until it is given access to samples of the nerve agent, and has made a formal request to the Foreign Office for an explanation about suggestions it will be hit by a cyber strike.
May is on Wednesday likely to outline the UK's response in the House of Commons, which could include a World Cup boycott, extra deployments of troops in Nato states bordering Russia, the expulsion of the Russian ambassador in London and fresh curbs on Russian finance in the UK. She will be informed by a summit of the UK's National Security Council earlier in the day.
The UK has been assured of the backing of the US, Germany and France as Britain's international allies have responded with condemnation over the nerve agent attack.
After the call between Trump and May, a No 10 spokesperson said: "The Prime Minister set out the conclusion reached by the UK Government that it was highly likely that Russia was responsible for the attack against Sergei and Yulia Skripal.
"President Trump said the US was with the UK all the way, agreeing that the Russian Government must provide unambiguous answers as to how this nerve agent came to be used."
A White House statement reiterated the need for "unambiguous answers", and warned of "consequences for those who use these heinous weapons in flagrant violation of international norms".
The conversation between the two allies comes as Britain has given Moscow until midnight to come up with with a "credible" explanation as to what happened after the UK government claimed it was "highly likely" Russia was responsible.
The prime minister has said if this is not forthcoming, the British government would conclude the attack was an unlawful "use of force" against the UK by Russia.
In a day a frantic diplomacy, Russia earlier demanded access to samples of the nerve agent that poisoned the former double agent and his daughter.
Foreign Minister Sergei Lavrov told reporters on Tuesday morning that Russia was "not to blame" for the attempted murder of the pair.
Home Secretary Amber Rudd earlier said Russia had "started responding" but the embassy appeared to suggest this amounted to little more than informing the Foreign Office of its demands and reiterating it was not involved.
Britain's ambassador to Russia was summoned by Moscow and told by first deputy foreign minister Vladimir Titov that the Kremlin "strongly protested" the accusations, the embassy said.
The Baltic states which border Russia, including Lithuania and Estonia, also offered their support in the wake of the attack.
Latvia said it was prepared to offer the "required support" and urged Nato and the EU to agree on action.
The UK will brief the North Atlantic Council, the main decision-making body at Nato, on Wednesday.
Meanwhile, a probe has been launched by counter-terrorism police amid reports a Russian exile who was a close friend of Putin critic Boris Berezovsky has been found dead.
Scotland Yard said a man in his 60s was found at a home in Clarence Avenue, New Malden, south-west London on Monday and that the cause of his death is unexplained.
In a further twist, Rudd said police and the security services would investigate allegations of Russian state involvement in 14 deaths over recent years in Britain, a letter published on Tuesday showed.
Last week, the chairman of parliament's Home Affairs Committee wrote to Rudd asking for a review of 14 deaths that were not originally treated as suspicious by police but had repeatedly been linked to Russia in media reports.
"I will want to satisfy myself that the allegations are nothing more than that," Rudd said in her response published on Tuesday. "The police and (the UK's domestic spy agency) MI5 agree and will assist in that endeavour."
As the investigation continues, police warned Salisbury residents the complex probe could take "many weeks" and they could see more cordons go up across the city as it continued.