The United States on Tuesday strongly condemned Russias renewed bombing campaign in Syria and warned that its strikes on civilian targets break international law.
State Department spokeswoman Elizabeth Trudeau said Washington had received reports that the latest Russian and Syrian regime strikes had hit hospitals and clinics.
"We strongly condemn the resumption of air strikes in Syria by the Russians as well as the Syrian regime," she told reporters.
"The most recent reported attacks are on five hospitals and one mobile clinic in Syria. We believe it's a violation of international law."
Earlier, Moscow said it had launched a "major operation" in support of Bashar al-Assad's Syrian regime, flying jets off its aircraft carrier in the Mediterranean.
An AFP correspondent in Idlib said strikes hit several parts of the rebel stronghold province, including Maaret al-Numan, Saraqib and Ariha.
Idlib is largely controlled by a rebel coalition that includes Fateh al-Sham, the former Al-Nusra Front, which both Washington and Moscow regard as an Al-Qaeda front.
But Trudeau said initial reports suggested civilian targets were among those hit and that the Russian-backed siege of eastern Aleppo was choking off aid shipments.
She accused Moscow of "letting eastern Aleppo residents starve while seeking praise from the international community for halting indiscriminate strikes."
"We have consistently tried to deescalate the violence in Syria, we're at the table on that again in Geneva today," the spokeswoman said, referring to multilateral ceasefire talks.
US President Barack Obama's administration has been talking to Russia about ways to reign in Assad's forces and find a ceasefire in Syria's brutal civil war.
"We believe that Russia and the Syrian regime's actions are inexcusable. However we still believe that the only way forward is a political resolution," Trudeau said.
But Russia's President Vladimir Putin insists Moscow's intervention is aimed at protecting a legitimate government against Al-Qaeda and the Islamic State group.
US President-elect Donald Trump, who is waiting to assume office on January 20, has already been in touch with Putin about normalizing US-Russian ties.
During the US presidential campaign Trump said his priority would be to defeat the Islamic State group and suggested working with Russia to that end.