John Kerry, the US secretary of state, has expressed US concern over reports of Russia's enhanced military build-up in Syria in a telephone call with his Russian counterpart, according to the US state department.
The phone call came a day after media reports quoted US officials as describing an increase in Russian military activity in Syria, expanding the country's support for Syrian President Bashar al-Assad.
"The secretary made clear that if such reports were accurate, these actions could further escalate the conflict, lead to greater loss of innocent life, increase refugee flows and risk confrontation with the anti-ISIL coalition operating in Syria," the state department said on Saturday, referring to the Islamic State of Iraq and the Levant.
It said Kerry and Sergey Lavrov, the Russian foreign minister, agreed that discussions on the Syrian conflict would continue this month in New York, where the UN General Assembly meets.
Quoting unidentified Obama administration officials, the New York Times said Russia has dispatched a military advance team to Syria and has sent prefabricated housing units for hundreds of people to a Syrian airfield and delivered a portable air traffic control station there.
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Assad's ancestral home
Some US officials said the temporary housing suggested Russia could deploy up to 1,000 advisers or other military personnel to the airfield that serves Latakia, Syria's principal port city that is near the Assad family's ancestral home, the New York Times reported.
It said officials see no indications Russia intends to deploy significant ground forces, but may be preparing the airfield as a base for transporting military supplies or a launching pad for air strikes supporting Assad.
The Los Angeles Times reported US intelligence has gathered evidence of possible military housing from satellite reconnaissance photos.
In recent weeks, there has been a flurry of diplomatic consultations to try to find a way out of the crisis, including a meeting in Doha, Qatar, on August 3 between the top US, Russian, and Saudi diplomats.
The Saudi and Iranian foreign ministers were later received separately in Moscow, as were representatives of various Syrian opposition groups.
Russia, which has been a bulwark of military and diplomatic support to the Assad government, is promoting an expanded coalition against ISIL that includes countries of the region as well as the regular Syrian army.
President Barack Obama for his part received Saudi King Salman on Friday for talks dominated by Syria. They advocate a political solution that would include Assad's departure from power.
On the ground in Syria, anti-government violence erupted on Saturday in a southern province that had largely stayed on the sidelines of the country's civil war.
The violence in Suweida province, a stronghold of the Druze minority sect, followed the killing of a prominent religious leader in rare explosions on Friday that claimed the lives of at least 25 others, activists and pro-government media said.
Rioters holding the government responsible for the death of Sheikh Wahid al-Balous destroyed the statue of late Syrian President Hafez al-Assad and besieged security offices, the Britain-based Syrian Observatory for Human Rights and other activist groups said.
Balous was a prominent critic of Assad and had called on youth in Suweida to refuse to serve in the military.
He was also a critic of ISIL fighters who have taken over a third of the country and are fuelling the civil war that has killed more than 250,000 people and wounded more than one million.
Balous died in one of two consecutive car bomb explosions, including one near the National Hospital in Suweida.
The Syrian Observatory said the death toll rose on Saturday to 37, including six security personnel killed in clashes with rioters.
Conflicting toll figures
Suweida had witnessed large rallies in the days before the explosions against the failure of the government to provide basic services. Activists reported that there was no internet service for the past few days.
Syria's official news agency and other activist groups put the death toll from the blasts at 26. There was no immediate claim of responsibly for the bombings.
Some of Balous' supporters said in a statement they would expel security forces from Suweida, which until now has largely stayed out of the fighting.
Elsewhere in Syria, at least 47 fighters have been killed in battles between ISIL and rebel groups, reports say.
The fighting was centred around the rebel-held town of Marea near the Turkish border.
Marea is within a proposed safe zone put forward by Turkey last month. If rebels lose the town, it will make it harder to clear ISIL from the area.
Source: Al Jazeera and agencies