US, Russia to hold military talks as Assad plans attack on Aleppo

Military commanders from Russia and the United States will hold another round of talks on Wednesday on how to stay out of each other's way in the skies over Syria, as the Syrian army revealed plans for a large-scale attack on the Aleppo province.

US Defence Secretary Ash Carter announced the latest "de-confliction" talks as jets from both countries pounded targets in the war-torn Middle Eastern country.

"Russia must act professionally in the skies over Syria and abide by basic safety procedures," Carter said in Boston after talks with his Australian counterpart.

"We'll have another conversation with the Russians tomorrow on this subject. Those discussions are progressing. Nothing has been finalised," he said. 

"Even as we continue to disagree on Syria policy, we should be able to at least agree on making sure our airmen are as safe as possible."

Carter would not put a time frame on the "de-confliction" talks, but added: "I expect that to conclude shortly."

And he warned the military-to-military dialogue would not lead to talks on Moscow's approach in Syria "because it is wrong-headed and strategically shortsighted".

Russia said on Tuesday its air force had hit 86 "terrorist" targets in Syria in the previous 24 hours, including several linked to the Islamic State (IS) group.

Washington and its allies - engaged in their own air war - accuse Moscow of targeting US-backed rebels who are fighting IS and al-Qaeda's affilitate, al-Nusra Front, and seeking to prop up Bashar al-Assad's government.

But Putin hit back, criticising Washington for refusing to share intelligence with Russia and accusing it of muddled thinking and a refusal to cooperate.

Meanwhile, Reuters reported that the Syrian army and allied forces were preparing for a large ground attack against rebels in the Aleppo area.

The ground attacks will be supported by Russian airstrikes and "thousands" of Iranian troops and Hezbollah fighters, two senior regional officials told Reuters on the condition of anonymity on Tuesday. 

"The decision to launch the battle of Aleppo has been taken," said one of the officials. "It is no longer hidden that thousands of Iranians are now in Syria and their role is fundamental."

Both officials said the attack would begin "soon," without providing further details.