WASHINGTON — The United States said Thursday it held "serious" talks with Russia about Syria and renewed its call for a political transition after months of disagreement over the bloodshed.

Wendy Sherman, the under secretary of state for political affairs, "had very serious discussions" in Moscow with senior officials, the State Department said in a statement, calling the talks "direct and fulsome."

Sherman explained US support for the decision to end a UN observer mission, which was "intended to monitor a ceasefire that does not exist."

"The beginning of a political process is in the international community's long-term interests," she added.

Russia is the main supporter of Syrian President Bashar al-Assad and the United States has repeatedly urged Moscow to do more to end the violence that activists say has claimed more than 23,000 lives in the past 17 months.

In turn, Moscow has accused Washington of prolonging the conflict through support for the opposition.

Russia's UN envoy Vitaly Churkin earlier said that nations refusing to back the UN observer mission "did not really show a commitment to ending hostilities."

Sherman, the State Department's number three, also spoke to Russia about Iran's contested nuclear program and said that "diplomacy still has a chance to succeed," the statement said.