Russia has warned of the risk of a “proxy war” in the Middle East after the US said it would send special forces to Syria.
Russian Foreign Minister Sergei Lavrov said this increased the need for co-operation between the US and Russia.
US officials said “fewer than 50” troops would “train, advise and assist” vetted opposition forces in fighting theISIS.
It will be the first time that US troops operate openly in Syria.
Mr Lavrov said the US had decided on its move “unilaterally and without any reference to the Syrian leadership”.
He added: “I am convinced that neither the United States nor Russia of course want any kind of slide into a so-called proxy war But to me it is obvious that this situation makes the task of co-operation between the militaries even more relevant.”
He was speaking after talks with US Secretary of State John Kerry and UN envoy for Syria Staffan de Mistura in Vienna.
“Our role fundamentally and the strategy is to enable local forces but does that put US forces in harm’s way? It does, no question about it,” Defence Secretary Ash Carter later told reporters.