US Secretary of State Mike Pompeo says there is a "substantial chance" that the suspected poisoning of Russian opposition figure Alexei Navalny was ordered by senior officials in Moscow, BBC News reported.

Pompeo said the US was evaluating how it would respond.

Pompeo gave his comments in an interview with US commentator Ben Shapiro, who asked if there would be any ramifications for the Russian government over apparent attacks on its political opponents.

The secretary of state said the US, along with the EU, had made clear to Russia "our expectations that they will hold those responsible for this accountable. We'll do our best to come to a conclusion about who was responsible, too."

"I think people all around the world will see this kind of activity for what it is," he added. "And when they see the effort to poison a dissident, they recognize that there is a substantial chance that this actually came from Russia."

He added that "the world has matured and come to an understanding that this is not how normal countries operate, and this will prove costly for the Russians."