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Russia could be planning a chemical or biological weapon attack in Ukraine - and "we should all be on the lookout", the White House has said.

Press secretary Jen Psaki said Russia's claims about US biological weapon labs, and chemical weapon development in Ukraine, were preposterous.

She called the false claims an "obvious ploy" to try to justify further premeditated, unprovoked attacks.

It comes after Western officials shared similar concerns about fresh attacks.

Correspondent David Grossman reports.

Christian Fraser is joined by shadow foreign secretary David Lammy and Conservative MP and member of the foreign affairs select committee, Bob Seely.