US President Joe Biden sought on Thursday to clarify US policy on a possible Russian invasion of Ukraine after his remarks about how America might respond to a "minor incursion" raised questions about US intervention.

"If any, any assembled Russian units move across the Ukrainian border, that is an invasion," Biden told reporters at the White House. It will be met by a "severe and coordinated" economic response that has been discussed in detail with allies and laid out to Russian President Vladimir Putin, he said...