Fighting between Syrian rebel and government forces eased on Saturday as a Russian-led effort to shore up a ceasefire took effect, although battles continued on important frontlines near Hama and Damascus, rebels and a war monitor said.
A de-escalation agreement in Syria will take effect at midnight on Friday but Russia's air force will continue strikes against the Islamic State (group) elsewhere in the country, Russian officials have said.
Syrian President Bashar al-Assad said a suspected chemical weapons attack was a "fabrication" to justify a US military strike, as Moscow digs in to defend its ally despite increasing strains with Washington.
US Secretary of State Rex Tillerson met with Russian President Vladimir Putin in Moscow on Wednesday as the two countries traded sharp accusations about a chemical weapons attack in Syria.
Russian President Vladimir Putin on Tuesday warned of future chemical weapons "provocations" in Syria to frame President Bashar al-Assad, just as Washington's top diplomat arrived for talks in Moscow.
A joint command centre made up of forces from Russia, Iran and militias backing Syrian President Bashar al Assad threatened reprisals against any party that carries out "aggression" against Syria, two days after US missiles hit a Syrian air base.