The talks “will focus on reducing violence, expanding humanitarian assistance for the Syrian people, and moving toward a political solution needed to end the civil war,” spokesman John Kirby said in a statement.

The diplomatic news came against a backdrop of continued military turmoil, with coalition-backed forces continuing to push the Islamic State group away from the Turkish border, an Islamist rebel leader dying in a bombing attack, and pro-regime forces making major gains on the outskirts of the ravaged city of Aleppo.

US Defense Secretary Ash Carter told BBC radio that there was “quite a long way to go” before a final peace deal could be struck.

He called for “a true cessation of hostilities - not what you’ve seen, which is a partial cessation of hostilities,” adding: “Our patience is not unlimited.”

Both sides have agreed that a deal must involve a durable ceasefire, humanitarian access to conflict-wracked areas and a resumption of peace talks.

Amid a flurry of diplomatic efforts, Turkish President Recep Tayyip Erdogan and Russian counterpart Vladimir Putin agreed to intensify efforts for a ceasefire “as soon as possible” in Aleppo, the Turkish news agency Anadolu reported.

Moscow backs the Syrian government of President Bashar al-Assad, while Ankara supports the opposition seeking his ouster.

US President Barack Obama earlier held talks with Putin on the sidelines of the G20 summit in China but the two, on opposite sides in Syria, failed to bridge their differences.

Lavrov suggested that problems in another part of the world - namely, US sanctions against Russia over the Ukraine crisis - may be hampering efforts between the former Cold War rivals to resolve “regional conflicts,” a reference to the Syrian war.

And Carter noted: “We have our differences, serious differences, with Russia elsewhere, especially here in Europe with Ukraine.”