The US and its allies are working to supply Ukraine with anti-ship missiles, a senior US administration official said, Reuters reports.

"We have started consulting with allies on providing anti-ship missiles to Ukraine," the official said on the sidelines of the NATO summit in Brussels. "There may be some technical challenges with making that happen but that is something that we are consulting with allies and starting to work on."

The official said Ukrainian President Volodymyr Zelenskyy joined NATO leaders by video link but did not repeat requests for NATO membership or a no-fly zone.

"The mood overall has been sober, it's been resolute and it's been incredibly united," the official said of the atmosphere at the summit meeting.