Ukranian President Volodymyr Zelensky (L) in Riga, Latvia, on October 16, 2019; and US President Joe Biden speaking on June 4, 2021, at the Rehoboth Beach, Delaware.

Ukraine war: Kyiv and Washington clarify leaders' nuclear remarks to calm fears

Kyiv says Zelenskyy called for 'pre-emptive sanctions' not a strike against Russia; the White House plays down Biden's warning about Moscow's nuclear threat — and other key developments.