U.S Vice President Joe Biden held talks with Russia's Foreign Minister Sergei Lavrov and UN-Arab League envoy Lakhdar Brahimi, at the Munich Security Conference Saturday, amid strong disagreement between Moscow and Washington about ways to end the 22-month Syria conflict. In Biden's meeting with Lavrov, he called on Washington and Moscow to put aside "serious differences" and stressed the need for US-Russian cooperation, including over Syria, the White House said. Earlier in Munich the U.S. vice president insisted Assad was a "tyrant" and must go. Biden also met Khatib and Brahimi in Munich on Saturday. He "urged Khatib to continue his efforts to maintain unity among the SOC (Syrian Opposition Coalition) leadership, to isolate extremist elements within the broader opposition, and to reach out to, and be inclusive of, a broad range of communities inside Syria, including Alawites, Christians and Kurds", according to a White House statement. Ground-breaking talks also took place between the Russian foreign minister and the Syrian opposition leader. It has bolstered a global push to narrow sharp differences over how to end the conflict in Syria. Moscow said Saturday it wanted to keep in regular contact with the Syrian opposition, after its Foreign Minister Sergei Lavrov and Syrian National Coalition leader Moaz al-Khatib met for the first time. "I reminded Khatib that after the creation of the coalition and the appointment of their leader, we immediately demonstrated our interest in maintaining regular contact," Russian news agencies quoted Lavrov as saying after the meeting on the sidelines of the Munich Security Conference. Khatib, who became the head of the coalition late last year, reiterated on the opening day of the Munich talks Friday an earlier surprise announcement that his group is ready for dialogue with the Damascus regime -- subject to conditions including the release of 160,000 detainees. Lavrov said Moscow welcomed the initiative, adding: "If we take into account the fact that the coalition was founded on a refusal to engage in a dialogue with the regime, it's a very important step." Moscow's engagement with the Syrian opposition comes just days after Russian Prime Minister Dmitri Medvedev took the rare step of criticising Syrian President Bashar al-Assad. Assad made a "grave, perhaps fatal error" in not reaching out more quickly to the Syrian opposition "which was ready to sit at the negotiating table with him", Russian news agencies quoted Medvedev as saying on Sunday last week. "It seems to me that his chances of staying (in power) are shrinking day by day," Medvedev told CNN television.