US President Donald Trump had earlier announced he would pull his country out of the 18-year-old pact between Russia, the US and 32 other nations, saying Moscow had not stuck to its commitments.

"I deeply regret the announcement," Maas said, adding that "we will work with our partners to urge the US to consider its decision".

He also said that Germany -- along with France, Poland and Britain -- had repeatedly explained to Washington that the difficulties on the Russian side in recent years "did not justify" pulling out.

Maas said the treaty "contributes to security and peace in almost all of the northern hemisphere" and would be "weakened" by the US withdrawal.

He also called on Russia to "return to fully implementing" the pact.

"We will continue implementing the treaty and do everything to preserve it," Maas said, adding he was coordinating closely with his European colleagues.

NATO ambassadors will hold an urgent meeting on Friday to discuss the development, a diplomat told AFP.

Moscow described it as a "blow" to European security.

The United States has been frustrated that Russia will not permit US flights over areas where Washington believes Moscow is deploying medium-range nuclear weapons that threaten Europe.

The treaty permits one country's military to conduct a certain number of surveillance flights over another each year on short notice.

The aircraft can survey the territory below, collecting information and pictures of military installations and activities.

The idea is that the more rival militaries know about each other, the less the chance of conflict between them.