General Joseph Dunford, the chairman of the Joint Chiefs of Staff, met with General Valery Gerasimov, the chief of the Russian General Staff, in Vienna, Dunford's spokesman Colonel Pat Ryder said.

"The two military leaders discussed the deconfliction of coalition and Russian operations in Syria, and exchanged views on the state of US-Russia military relations and the current international security situation in Europe and other key topics," Ryder said in a statement.

Since Russia's entry into the Syria conflict in 2015, Moscow and Washington have "deconflicted" their respective operations against IS, warning each other of planned air operations to avoid contact.

"Both leaders recognize the importance of maintaining regular communication to avoid miscalculation and to promote transparency and deconfliction in areas where our militaries are operating in close proximity," Ryder said.

The meeting -- the first since June -- comes amid heightened tensions between the United States and Russia, with the Pentagon pursuing a renewed focus on Russia as a "great power" competitor.

Russian President Vladimir Putin on Monday officially suspended Russia's participation in the Intermediate Range Nuclear Forces (INF) treaty, a key Cold War-era arms agreement, after Washington first moved to ditch the deal.

The INF treaty eliminated short- and medium-range ballistic missiles, cruise missiles and missile launchers from Europe.

Despite the conflict in Syria and the rising bilateral tensions, the military chiefs have kept open a channel of communications.

In August 2018, Russia sent a confidential letter, which leaked, containing proposals for cooperation to assure Syria's reconstruction and the return of refugees.

President Donald Trump decided in December to withdraw US troops from northeastern Syria, where they had fought alongside Kurdish forces against IS jihadists, but he has since agreed to leave behind a residual force of about 200 US troops.

Washington is currently negotiating with Western allies in the anti-IS coalition on an international force that would train security forces capable of stabilizing parts of Syria.