MUNICH -- The annual Munich Security Conference (MSC) has seen intense debates on Saturday between top diplomats from western countries and Russia, showing significant differences between the two sides on major security issues.

MSC, the most important informal meeting on security policy, entered its second day on Saturday, welcoming representatives of countries that are standing in focus of the global security, including Russian Prime Minister Dmitry Medvedev, US Secretary of State John Kerry and Ukrainian President Petro Poroshenko.

Speaking during a Prime Ministers' Debate, Medvedev warned of "new Cold War," saying the West often uses deterrent means and its policy against Russia is "unfriendly," which has resulted in a break-down of dialogue between the two sides.

Medvedev criticized the expansion of NATO and EU influence into Eastern Europe.

"European politicians thought that creating a so-called belt of friends at Europe's side, on the outskirts of the EU, could be a guarantee of security, and what's the result?" he said. "Not a belt of friends but a belt of exclusion."

Speaking of Russia's role, NATO General Secretary Jens Stoltenberg said earlier in a statement that "we have seen a more assertive Russia, a Russia which is destabilizing the European security order."

"NATO does not seek confrontation and we don't want a new Cold War. But at the same time our response has to be firm," Stoltenberg added.

Different positions on Syria and Ukraine have undermined the relations between Russia and the West. Both sides posed sanctions against each other.

Speaking of the conflict in Syria, Kerry stressed in his speech the need to negotiate a political solution to the issue, but insisted that Syrian President Bashar al-Assad must step down.

Medvedev, who had visited Syria before the conflict started, told the conference that Syria was once a peaceful country, and it would have the chance to continue to enjoy the fruits of economic development if there was no external influence.

"People from the US and European countries said al-Assad must go... but the country has been in a state of war for years... Who should be blamed for that?" he further said.