Russia's prime minister accused the West on Saturday of rekindling the Cold War, telling a meeting of top defense officials, diplomats and national leaders that sanctions imposed after the annexation of Crimea and new moves by the NATO alliance "only aggravate" tensions.

Dmitry Medvedev said Russian President Vladimir Putin told the same Munich Security Conference in 2007 that the West's building of a missile defense system risked restarting the Cold War, and that now "the picture is more grim; the developments since 2007 have been worse than anticipated."

"NATO's policies related to Russia remain unfriendly and opaque — one could go so far as to say we have slid back to a new Cold War," he said.

NATO Secretary General Jens Stoltenberg threw the blame back at Moscow. "Russia's rhetoric, posture and exercises of its nuclear forces are aimed at intimidating its neighbors, undermining trust and stability in Europe," he said.

The annual conference is one known for frank talk among top officials, and participants this year include U.S. Secretary of State John Kerry, French Prime Minister Manuel Valls, Ukrainian President Petro Poroshenko, Russian Foreign Minister Sergey Lavrov, British Foreign Minister Philip Hammond, and many others.

Medvedev's comments came shortly after Stoltenberg told the group that in response to a "more assertive Russia... which is destabilizing the European security order" the alliance does "not want a new Cold War but at the same time our response has to be firm."

Stoltenberg stressed the need for dialogue, but also defended NATO's move to strengthen defenses, including moving more troops and equipment to countries bordering Russia, and said at an upcoming summer summit in Warsaw he expected member countries "to decide to further strengthen the alliance's defense and deterrence."

He underlined that NATO's deterrent also included nuclear weapons, saying "no one should think that nuclear weapons can be used as part of a conventional conflict — it would change the nature of any conflict fundamentally."

Medvedev scoffed at what he said was a suggestion that Russia may use nuclear weapons in a first strike, saying "sometimes I wonder if it's 2016 or if we live in 1962."

He called for sanctions on Russia implemented after it annexed Crimea from Ukraine in March 2014 to be lifted, saying they were "a road that leads nowhere."

Earlier in the day, Medvedev suggested the West would harm itself if it did not lift the sanctions soon.

"The longer the sanctions continue chances for the Europeans to keep their position at the Russian market as investors and suppliers are fading," he said. "That's why one has to act quickly."