The United States said that recent raids by Russia in Syria had "caused collateral damage," including at a hospital, which NGOs have reported but Moscow has denied.
"We've some information that would lead us to believe that Russian military aircraft did hit a hospital," State Department spokesman John Kirby told reporters.
Last Thursday (local time), Russia called reports of the strike on a clinic "fake", attacking the British-based Syrian Observatory for Human Rights for reporting the information.
The monitoring group said that 13 people including medical staff were killed in Russian air strikes on October 20 against a field hospital in the northwestern province of Idlib that was run by the Syrian-American Medical Society.
Also last Thursday, the society itself, which operates several facilities in Syria, accused Russia of carrying out nine air strikes that hit five hospitals or field clinics in areas held by rebels, killing civilians and medical personnel.
"We have other operational information that leads us to believe that Russian targeting has not only not been focused on ISIL (the Islamic State group), but has in fact, caused collateral damage and some civilian casualties to include some civil infrastructure," Kirby said.
However, he gave no more specifics and declined to say whether the direct information obtained by the United States was transmitted by Russia.
Russian and US forces both perform military operations in Syria's airspace and exchange information to avoid air accidents.
Russia began its air campaign in Syria on September 30 in support of its ally President Bashar al-Assad.
The campaign has been criticised by the United States not only for causing civilian casualties but for targeting non-jihadist rebel groups more than the Islamic State group or Al-Qaeda.
The United States, Russia and other major backers of Syria's warring rivals, including Iran, are seeking to narrow divisions over the future of the country and its embattled president at a two-day round of international talks that began Thursday in Vienna.
More than 250,000 people have died in Syria's war since it began in March 2011 following a bloody crackdown on protests against Assad's rule.