Russia's decision to pull out some of its troops from Syria has raised hopes that it could help move the peace talks in Geneva forward.
Moscow began moving out military equipment and personnel on Tuesday but said it planned to keep 800 soldiers in the country for reconnaissance and to protect its military bases in Syria.
With Russia's decision to remove "half its forces immediately" from Syria, along with the beginning of peace talks, US Secretary of State John Kerry said that "this is a moment to seize, not waste."
Kerry plans to travel to Moscow next week to meet with Russian President Vladimir Putin and Foreign Minister Sergei Lavrov and to discuss how to move the political process on Syria forward.
Only a small number of Russian aircraft had returned home so far, and Russian airstrikes had continued in the past 24 hours, US Pentagon spokesman Peter Cook pointed out.
German Foreign Minister Frank-Walter Steinmeier said that Syrian President Bashar al-Assad was coming under pressure as his Russian ally was partially pulling out from the conflict.
"This announcement is a signal for Assad that the time has finally come to negotiate seriously in Geneva," Steinmeier said in Berlin.
According to the United States, Russia's aerial campaign that started in September has targeted Western-backed rebels along with extremist groups such as Islamic State.
UN-brokered talks involving Syrian government and opposition delegates resumed Monday in Geneva, after Washington and Moscow had brokered agreements on a ceasefire and on humanitarian aid deliveries.
"We want all foreign forces to leave Syria," opposition delegation spokesman Salim al-Muslat told reporters at the talks.
"We want friends and visitors, but not people who help to kill people," he added.
By Tuesday, both the opposition and the government side had submitted proposals for a political transition to UN mediator Staffan de Mistura, who has been shuttling between the two sides.
De Mistura said the Syrian refugee crisis, Russia's military intervention and the strength of Islamic state extremists in the conflict had produced a new momentum for talks.
"There has been a sense of urgency," he said.
The latest Russian move would hopefully help achieve a political solution to the war and a transition process, he said.
"If he can be hopeful, we can be hopeful," opposition delegate Bassma Kodmani reacted.
The opposition demanded that de Mistura and influential powers push for prisoner releases as an urgent confidence-building measure.
De Mistura said the humanitarian aid task force of global and regional powers could deal with this issue.
Putin declared Monday that the military would begin withdrawing most of its forces because their task had been "completely fulfilled."
"Russia's biggest risk in the Syria operation was to be dragged into a long-term military conflict. As we see, that did not happen," prominent Russian political analyst Yevgeny Minchenko told Interfax news agency.
But some troops need to stay behind to protect Russia's airbase in the Syrian province of Latakia and its naval facility in the province of Tartus, the head of the upper house of parliament's defence committee, Viktor Ozerov, said.
Russia also retained the right to conduct aerial reconnaissance, and could maintain S-400 missile defence systems in Syria for additional defence, he said.
Al-Muslat, the opposition spokesman, said that all other foreign troops should also leave, without naming any countries.
Iranian fighters and members of the Lebanese Hezbollah milita are fighting alongside al-Assad's forces, while some Western and regional powers including the United States support rebel groups.