The US and Russian military will hold talks “as soon as possible” to avoid clashing in Syria, the countries’ top diplomats say.
Russian defence officials say their aircraft carried out about 20 missions against the so-called Islamic State group (IS) on Wednesday.
But the US expressed fears the targets were non-IS opponents of Russia’s ally, Syrian President Bashar al-Assad.
The US is targeting IS with air strikes in both Syria and Iraq.
Nato said there had been little co-ordination by Russia with US-led forces against IS, also known as Isil. The US says it was informed of Wednesday’s air strikes only an hour before they took place.
The New York Times and the Wall Street Journal report that the Russian strikes targeted US-backed rebels, including some trained by the CIA.
Are the Russians trying to destroy IS or are they trying to prop up President Assad? The Americans see the two as very different, the Russians less so.
On the evidence of one day’s bombing, it looks to be very much the latter. The target of Russian ordnance has been in places where IS has no presence.
In other words, other rebel groups – any rebel groups – opposed to President Assad are being targeted. And that raises another huge question. What if the Russians start hitting US-backed and armed rebel groups? That is not going to end well.
Diplomatic goals behind Putin’s Syria build-up
Russia’s Foreign Minister Sergei Lavrov said there was a need to “establish channels of communication to avoid any unintended incidents”. His US counterpart, John Kerry, said talks will be held “as soon as possible,” maybe as early as Thursday.
Mr Kerry added: “It’s one thing to be targeting Isil, but the concern, obviously, is that this is not what was happening.”
France’s Defence Minister, Jean-Yves Le Drian, told French MPs: “Curiously, they didn’t hit Islamic State. I will let you draw a certain number of conclusions yourselves.”
US Defence Secretary Ashton Carter said Russia’s approach was “tantamount to pouring gasoline on the fire” and “doomed to fail” because of the breadth of Syrian opposition to Mr Assad.