The trio had turned to the court after losing close relatives to a drone attack in 2012 in Hadramaut province.

Pointing to the significance of the US airbase in the German town of Ramstein for drone deployments in Yemen, they took their case to Germany, seeking to make Berlin stop Washington from using the base in such unmanned missions.

On Tuesday, the court rejected their call for the German government to outlaw the involvement of Ramstein in drone attacks on Yemen.

At the same time, the court ordered Berlin to take "appropriate measures to ascertain if the use by the US of the Ramstein airbase in armed drone deployments at the residence of the plaintiff in Yemen complies with international laws".

"If necessary, Berlin would have to work with the US towards compliance (with international laws)," the court said in a statement, stressing that Germany has a responsibility to protect lives.

The court said there was "clear factual evidence" showing that the US was using Ramstein base in drone missions in Yemen that "at least partially violated international law".

As such, "the plaintiffs' right to life is unlawfully endangered", it said.

Andreas Schueller of the European Center for Constitutional and Human Rights which backs the plaintiffs, said the ruling was an "important step towards placing limits on the drone programme as carried out via Ramstein".

"Germany must now face up to its responsibility for these strikes," he said.

The US is supporting a Saudi-led coalition fighting against Iran-backed Huthi rebels in Yemen.

Besides intelligence support, Washington has been supplying bombs and other weapons to the coalition.