US Secretary of State Rex Tillerson says the poisoning of ex-spy Sergei Skripal in Britain "clearly came from Russia" and "certainly will trigger a response."
Tillerson says he doesn't know whether Russia's government had knowledge of the poisoning. But he is arguing the poison couldn't have originated anywhere else. He says the substance is known to the US and doesn't exist widely. He says it's "only in the hands of a very, very limited number of parties."
Tillerson calls the poisoning "a really egregious act" and says it's "almost beyond comprehension" that a state actor would use such a dangerous substance in a public place.
But he says he won't elaborate on what response might follow.
Tillerson spoke to reporters on his aircraft as he flew from Nigeria to Washington.