"We are working very hard with Russians and we are fairly encouraged by what's going on there," McGurk said, referring to the achieved ceasefire in southwestern Syria.
McGurk added that Syria presents a far more complex challenge to the coalition than Iraq because they do not have contacts with the government in Damascus.
Recent de-escalation efforts have been a welcome development, McGurk said.
The southwestern Syria ceasefire entered into force at noon Damascus time on Sunday after an agreement had been reached by Russia, the United States and Jordan.
The deal was announced by Russian Foreign Minister Sergey Lavrov on June 7 after the first face-to-face meeting between Russian President Vladimir Putin and US President Donald Trump. McGurk called the meeting between Putin and Trump a "very productive discussion."
Moscow and Washington have committed themselves to ensuring the implementation of the ceasefire.
McGurk made remarks at an open session on the heels of three days of talks between leaders of the global coalition to defeat IS in Washington, DC.
