Russian air strikes in and around the city of Aleppo against opponents of the Syrian regime are benefitting the Islamic State group, a senior US official charged Wednesday.

"What Russia's doing is directly enabling ISIL," Brett McGurk, President Barack Obama's special envoy to the coalition fighting the group in Syria and Iraq, told the House Foreign Affairs Committee.

US Secretary of State John Kerry has taken the lead over the past week in accusing Russia of derailing efforts to get Syrian peace talks going, by carrying out air strikes around Aleppo in support of a government offensive.

Kerry and some 20 foreign ministers, including Russia's Sergei Lavrov, are meeting in Munich Thursday to try to arrange a ceasefire and humanitarian access to Syrian cities besieged by government forces.

On Tuesday, Kerry called on Moscow to work for an immediate ceasefire in Syria and to halt its air campaign, which has intensified in recent days.

The US-led coalition has waged a separate air campaign against IS since September 2014.

Russia, Syrian President Bashar al-Assad's closest ally, began conducting air strikes of its own September 30, 2015, targeting mainly rebels backed by the West, according to US officials.

In his testimony, McGurk outlined coalition plans to intensify its campaign against IS in Iraq and Syria, acknowledging the complexity of the task because it relies heavily on a diverse array of local forces on the ground.

"This is extremely difficult, but now doable. Our progress will not always be linear, and we should expect setbacks and surprises," McGurk said in his written testimony.