NATO Secretary General Jens Stoltenberg discussed the situation in Ukraine with Russian Foreign Minister Sergei Lavrov on Tuesday.

According to a NATO statement, Stoltenberg expressed the very strong NATO position on "the annexation of Crimea", also on the very serious situation in eastern Ukraine at the meeting.

The NATO chief underlined the importance of full implementation of the Minsk Agreements.

They also talked about transparency and predictability of military exercises.

NATO concluded an annual anti-submarine exercise in northern Europe on Monday. In Estonia, over 13,000 troops from eight NATO countries were taking part in a major land exercise. "These are just a few examples of how NATO provides deterrence," Stoltenberg said earlier this month.

In addition, both sides addressed the question of military lines of communications.

"It is important to have these lines of communication and also they can contribute to more predictability and avoiding any misunderstandings," Stoltenberg said.

NATO has suspended all practical cooperation with Russia as a response to the Crimea crisis in April 2014, leaving the lines of political contact open.

Meanwhile, Kiev has long accused Moscow of aiding pro-independence insurgents in eastern Ukraine and sending troops to combat areas in the restive Lugansk and Donetsk regions.

Moscow has repeatedly dismissed Kiev's claims, saying that Ukraine has offered no evidence of Russia's alleged involvement in the conflict, which has killed over 6,100 people since April 2014.