Doubt's been cast on claims that sanctioned Russian oligarch and Chelsea Owner Roman Abramovich and Ukrainian peace negotiators were victims of a poisoning earlier this month

The investigative website Bellingcat, which uncovered details about the Salisbury spy poisonings, says they suffered eye and skin pain.

But a US official says its own intelligence suggests an environmental factor was to blame instead.

The country has previously said that the use of chemical weapons would trigger a response from it.