NATO Secretary General Jens Stoltenberg reiterated that Russian forces are inside eastern Ukraine, however, he did not comment on specific figures previously named by Ukrainian President Petro Poroshenko.

"I will not go into specific figures or numbers, partly because what we have seen is that the Russians have moved forces back and forth and they have a high number of forces on the border," he said at the joint press point with the Prime Minister of Norway, Erna Solberg, on Wednesday.

"For several months, we have seen the presence of Russian forces in eastern Ukraine. And we also see a substantial increase in the number of Russian heavy equipment there. And we speak about equipment like tanks, artillery, armored vehicles, advanced air defense systems and this Russian military presence with forces and equipment in eastern Ukraine does not contribute to a peaceful and negotiated solution," Stoltenberg stressed.

He called on Russia to stop its support for separatist forces, to respect its international obligations and to uphold the Minsk agreements.

"And what NATO is doing is that we are of course supporting Ukraine. We have the trust funds, we have provided, we give strong political support and we have also implemented our own assurance measures to underline that NATO is ready to protect and defend all Allies in the situation we see in Europe today," the NATO Secretary General said.