The Russian prime minister has accused the West of rekindling the Cold War.
He told senior defence officials and national leaders that sanctions imposed after the annexation of Crimea and new moves by Nato “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 defence 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 neighbours, undermining trust and stability in Europe.”
Ukraine’s president said Russia is living in a “completely different universe” and pointed to the risk of an “alternative Europe” led by Mr Putin.
Petro Poroshenko criticised Russia’s actions in Ukraine and Syria and said they are “a demonstration that we live in a completely different universe with Russia”.
He said the main danger to Europeans is an “alternative Europe with alternative values” such as isolation, intolerance and disrespect of human rights, adding: “This alternative Europe has its own leader. His name is Putin.”
The annual conference is known for frank talk among officials, and participants this year include US secretary of state John Kerry, French prime minister Manuel Valls, Russian foreign minister Sergey Lavrov and UK Foreign Secretary Philip Hammond.
Mr Medvedev’s comments came shortly after Mr Stoltenberg told the group that in response to a “more assertive Russia… which is destabilising the European security order”, the alliance does “not want a new Cold War but at the same time our response has to be firm”.
Mr Stoltenberg stressed the need for dialogue, but also defended Nato’s move to strengthen defences, including moving more troops and equipment to countries bordering Russia, and said that at a summer summit in Warsaw he expected member countries “to decide to further strengthen the alliance’s defence and deterrence”.
He underlined that Nato’s deterrent 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”.
Mr Medvedev scoffed at what he said was a suggestion that Moscow 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, Mr 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. That’s why one has to act quickly.”
Mr Kerry criticised Russia for its actions in Ukraine and Syria, accusing Moscow of “repeated aggression” in both places.
He said Russia is defying the will of the international community with its support for separatists in eastern Ukraine and its military intervention in Syria on behalf of President Bashar Assad.
Mr Kerry praised European nations for holding firm on the Ukraine sanctions and urged Moscow to act in good faith in forging a truce in Syria and allowing a political transition.
