Washington's envoy has warned that U.S. President Donald Trump could skip the upcoming NATO summit if other members of the defense alliance do not act on burden-sharing, the Spiegel news magazine reported on Friday, citing European diplomatic sources.

Germany in particular has come under pressure to boost its defense spending considerably, with U.S. Defence Secretary Pete Hegseth having spoken with his German counterpart Boris Pistorius on the issue last week, the report added.