Secretary of State John Kerry said he will travel to Moscow next week to discuss Russia's withdrawal of forces from Syria and the political transition process in the war-torn country.

Kerry said Tuesday he would meet Russian President Vladimir Putin with an eye toward pushing peace talks forward in light of the new development, saying "we have reached a very important phase in this process."

Earlier Tuesday, warplanes and troops stationed at Russia's air base in Syria started leaving for home after a partial pullout order from Putin the previous day, a step that raised hopes for progress at newly reconvened U.N.-brokered peace talks in Geneva.

Putin's announcement took the U.S. and many of its allies by surprise. U.S. officials have said they are cautiously optimistic about what the withdrawal may mean.