Unconfirmed reports about Russia possibly planning to expand its military support for Syrian President Bashar Assad has prompted a warning from the U.S. that such actions could lead to a clash with coalition forces.

The State Department issued a statement after Secretary of State John Kerry called Russian Foreign Minister Sergey Lavrov to express concern over the rumors “suggesting an imminent enhanced Russian military build-up” in Syria.

The State Department said Kerry made it clear to Lavrov in their conversation that such actions “could further escalate the conflict, lead to greater loss of innocent life, increase refugee flows and risk confrontation” with the anti-Islamic State coalition led by the U.S. that is carrying out airstrikes in Syria. However, the State Department didn’t elaborate or confirm the accuracy of those reports.

Russia has been an ally of Assad throughout Syria’s civil war and has provided diplomatic support and weaponry to help the Syrian leader maintain his grip on power. Moscow also maintains a small naval facility at the Syrian port of Tartous on the Mediterranean Sea.

Meanwhile, anti-government violence erupted on Saturday in the southern Syrian province of Sweida. The violence followed the killing of prominent cleric Sheik Wahid Balous in an explosion, which also claimed the lives of at least 25 others. Rioters holding the government responsible for the cleric's death 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 died in one of two consecutive car bomb explosions, including one near the National Hospital in Sweida. He was strong supporter of the rebels trying to topple Asasd.

The Observatory said the death toll rose Saturday to 37, including six security personnel killed in clashes with rioters. The city 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.

The Syrian government called the blasts “cowardly terrorist acts.” A police commander in the city, Mohammed Samra, said Sweida was “calm and stable” and denied any unrest, saying reports of violence were aimed at undermining security in the area.

Some of Balous' supporters said in a statement they will expel security forces from Sweida province, which until now has largely stayed out of the fighting in Syria's civil war.

City elders appealed for calm, warning against attempts to drag the province toward violence. Another statement from the city's Druze leaders urged supporters to be patient as the cleric's brother, who was seriously wounded in the attack, recovers.

A 10th century offshoot of Shiite Islam, the Druze made up about 5 percent of Syria's prewar population of 23 million people, and is split between supporters and opponents of Assad.

In neighboring Lebanon, which also has a sizeable Druze population, the sect's political leader Walid Jumblatt said Balous's death was a "painful strike" to the community.

"It is time for the honorable citizens (of Sweida) to rise up in the face of the Syrian regime that wants repression and to spread sedition," he told the anti-government Syrian Orient TV.

The National Syrian Coalition opposition group in exile also blamed the Syrian government for the killing of the cleric, known as "the Dignity Sheikh," saying it was part of an attempt to stop the anti-government protests in recent days. In a statement, coalition member Suheir Attasi said killing Balous only "increased the popular anger in the province."

The Associated Press contributed to this report.