Free Syrian Army says didn't refuse Russian military support

US Secretary of State John Kerry has travelled to Saudi Arabia for talks with King Salman expected to focus on the four-year-old conflict in Syria.

"The Syrian leadership must establish working contact with the opposition who are ready for dialogue", he said, "and, as much as I understood from our conversation the day before yesterday with President Assad, he is prepared for such a dialogue".

David Deptula, a retired three-star Air Force general who led planning for the air war in Operation Desert Storm, said the rates for American fighters in combat zones has been above 90%.

It is still unclear what Russia's military plan in Syria is - and if President Putin, despite his denials, intends to continue deploying more soldiers in the campaign in order to decisively back Basher Assad. Assad's term expires in 2021.

A member of the Russian delegation said Sunday that Assad had expressed a willingness to hold new parliamentary and presidential elections, but only after Syria is "liberated" from Islamic State group jihadists.

Lavrov said Russia's air force would be ready to help units of the "patriotic opposition" in Syria - specifically the Free Syrian Army, rebels supported by the United States - if it knew their whereabouts. It is also noteworthy that the dynamic Russian diplomacy reflects the clarity in Moscow's vision, which seeks to achieve a political solution in Syria.

Kirby acknowledged that Assad's future was "a key sticking point that needs to be resolved".

FSA commander Lt. Col. Ahmed Saoud scoffed at the suggestion, saying "Russia must first admit that the regime of Assad must go".

"What we care about is Assad leaving, not turning this from a war against the regime to a war against terrorism", said Saoud, a defected army officer who leads the 13th Division group.

"For deployed forces, that's a ugly rate", said Richard Aboulafia, an aviation analyst at the Teal Group, an aerospace consulting firm.

"Civilians in northern Homs may have nowhere to hide or flee as the offensive intensifies", said Nadim Houry, deputy Middle East director at Human Rights Watch.

Lavrov, whose interview was recorded on Thursday but only released on Saturday, called Washington's refusal to coordinate its Syria campaign with Moscow "a big mistake".

The two exchanged views on "all the questions associated with resolving the Syrian crisis, including four-way talks", between Russian Foreign Minister Sergei Lavrov and his USA, Turkish and Saudi counterparts, it said. They also see it as a way for Putin to try to project Russian influence more widely, a goal he appeared to achieve on Sunday with Iraq's announcement that Russia, Iran, Syria and the Iraqi government were sharing intelligence on Syria.

Kirby said Iran's role in the Syrian conflict, including its support for Assad and Lebanon's Hezbollah, was unhelpful.

Saudi Arabia's foreign minister, Adel al-Jubeir, insisted after the meeting that Assad should have no role in Syria's future, adding there had been a few progress in global talks on resolving the conflict.