Ukrainian President Volodymyr Zelensky and the US embassy in Kyiv issued warnings about the risk of a major Russian airstrike in the coming hours.
Their alerts came after Russian officials said the death toll from a Ukrainian strike on a college and its dormitory in a Russian-occupied town in eastern Ukraine had risen to 18.
Zelensky said they were checking the information, adding: "We are seeing signs of preparation for a combined strike on Ukrainian territory, including Kyiv, involving various types of weaponry."
The US embassy in Kyiv said it had "received information concerning a potentially significant air attack that may occur at any time over the next 24 hours".
Both Zelensky and the US embassy in their messages called on their citizens to seek shelter in the event of an air alert.
