"The obvious place to resettle them is America because they're less likely to be killed there and it's easier to protect them there under a new identity," an "intelligence source familiar with the negotiations" was reported as saying.

"There's a preference for them to be resettled in a five-eyes nation because their case would have huge security implications," the source added.

Britain's Foreign Office had no immediate comment on the report.

For Britain to help the pair, a senior police officer will first issue the Skripals with a so-called "Osman warning", a formal notification that intelligence suggests there is a real and immediate "threat to life".

They could be placed under a witness protection program that could involve moving them to a "safe house" and, in exceptional circumstances, they could be given round the clock armed police protection and even receive new identities.

Relations between Russia and Britain have plunged to their lowest in decades since the pair were found slumped unconscious on a bench in Salisbury on March 4.

The Russian embassy in London has sent a request for a meeting of its envoy with British foreign minister Boris Johnson to discuss the case, the RIA news agency reported on Saturday.

"We hope for a constructive response from the British side and are counting on such a meeting in the very nearest future," the agency cited a spokesman for the Russian embassy saying.

The Foreign Office confirmed it had received the request for ambassador Alexander

to meet Johnson, but called the request a diversionary tactic.

"We will be responding in due course," it said in a statement.

Yulia, a Russian citizen, had arrived in Britain only the day before to visit her father, who has been living in Britain for some seven years.

Both were found by Britain to be suffering from the effects of poisoning by a nerve agent but they are now recovering in hospital.

Britain blamed Russia for the alleged poisoning, calling it attempted murder, and asked Moscow to explain what happened but Russia denies any involvement and has suggested Britain itself carried out the attack to stoke anti-Russian hysteria.

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The attack prompted the biggest Western expulsion of Russian diplomats since the Cold War as allies in Europe and the United States sided with London's view that Moscow was either responsible or had lost control of the nerve agent.

Moscow has hit back by expelling Western diplomats, questioning how Britain knows that Russia was responsible and offering its rival interpretations, including that it amounted to a plot by British secret services.

Reuters, Telegraph, London