National Security Adviser Condoleezza Rice arrived in Moscow Sunday for discussions on deepening U.S.-Russian cooperation in spite of deep differences over the war in Iraq.

A White House official confirmed a Russian report that Rice was to meet with Defense Minister Sergei Ivanov, Foreign Minister Igor Ivanov and Russian Security Council chief Vladimir Rushailo. Another official, White House spokesman Taylor Gross, said President Bush spoke to Rice while she was in Moscow on Sunday.

"We are committed to our long-term strategic partnership with Russia," a U.S. Embassy spokesman said. "We've been through some difficult times, and differences over Iraq have strained the relationship."

Moscow has been strongly opposed to the U.S.-led war, and Russian officials and media alike have often poured derision on U.S. actions. However, Russian President Vladimir Putin has struck a softer tone over the past week, saying that a U.S. defeat in Iraq would not be in Moscow's interests and pledging to continue cooperation with the United States.

On Saturday, he said his administration would urge lawmakers to ratify a key nuclear arms reduction treaty with the United States, which the lower house of parliament indefinitely postponed last month as a sign of protest ahead of the imminent war.

Some analysts say the change in tone reflects Russia's hope of winning a role in Iraq's postwar reconstruction, as well as preserving its existing economic ties with the United States.

Rice plans to link up with Bush during his trip Monday to Belfast, where the president was to meet with British Prime Minister Tony Blair.