“Russia has some very serious questions to answer,” NATO Secretary General Jens Stoltenberg said, after reports of the death of leading Russian opposition figure Alexei Navalny.

Stoltenberg described Navalny as a “strong voice for freedom” and said NATO has called for his release from imprisonment for a long time.

The top NATO official declined to draw a link to the upcoming Russian presidential election but noted Russia “has become [a] more and more authoritarian power” for many years.

“I’m deeply saddened and very concerned,” Stoltenberg said.