"Germany must do more. And we cannot ensure the defense of the West if our allies grow dependent on Russia," Pence told a forum as part of two days of alliance events in Washington.

"It is simply unacceptable for Europe's largest economy to continue to ignore the threat of Russian aggression and neglect its own self-defense and our common defense," Pence said.

President Donald Trump has repeatedly voiced annoyance that Germany is not on track to meet a goal set by NATO in 2014 of each member spending two percent of GDP on defense.

Pence highlighted a report to parliament on Germany's armed forces, saying it showed "glaring deficiencies" in military readiness.

Germany, despite political concerns about Russia, has forged ahead with the Nord Stream 2 gas pipeline that would double the capacity of the existing link with Russia.

"If Germany persists in building the Nord Stream 2 pipeline, as President Trump said, it could turn Germany's economy into literally a captive of Russia," Pence said.

Germany, which opposes nuclear power, is eager for the added energy, but the pipeline is also opposed by the Baltic States and Poland which are wary over Russia due to past history.