BEIRUT — Russian warplanes are carrying out more airstrikes in support of Syrian government ground troops as rebels are firing more U.S. anti-tank weapons, deepening the impression that a proxy war between the United States and Russia is joining the list of interlocking conflicts in Syria.
Russia doubled the number of its airstrikes over the weekend to more than 60 a day, Russian state news media said, helping government troops take two villages Monday.
Videos posted online by pro-Russian outlets, from an area above the village of Tal Skayk, in Hama province, showed Syrian troops and allied militias watching as heavy barrages sent smoke towering from clusters of houses, while a narrator enthusiastically described progress in fighting "terrorists."
At the same time, the handful of insurgent groups that received covert assistance from the United States have intensified their use of TOW anti-tank guided missiles, posting more than two dozen videos in the past few days of the missiles weaving over open fields before hitting their targets.
Russia and the United States have both said that they are fighting militants of the Islamic State, also known as ISIS or ISIL, but the two countries support opposite sides in the battle between President Bashar Assad and Syrians who are rebelling against his government.
The dynamic has ratcheted up the dangers of the conflict, while also bolstering morale for combatants on both sides, because the higher stakes have led some fighters to expect stronger commitments from their backers.
With air support from Russia, Assad's government is trying to retake territory seized this year by insurgent groups that include the Nusra Front, the Syrian affiliate of al-Qaida, and U.S.-backed units calling themselves the Free Syrian Army.
But the insurgents in that area do not include the Islamic State, which declared the formation of a caliphate, or religious state, in June 2014 that stretches from northern and eastern Syria into Iraq.
The advances that have posed the most serious threat to Assad have come from a coalition of Islamist insurgents called the Army of Conquest that includes the Nusra Front but not the Islamic State.
Advancing alongside the Islamist groups, and sometimes aiding them, are several relatively secular groups led by army defectors, known as the Free Syrian Army.
The Free Syrian Army, despite fluctuating levels of assistance from the United States and its allies, has long been seen as a marginal player. The influence of Islamist groups has risen alongside better organization and financing. But new developments have given the Free Syrian Army a more prominent role, even while putting the group in new danger.
Several U.S.-aided units have come under direct fire by the Russians, but they claim to have held their territory, with the help of TOW missiles, better than their Islamist counterparts.
"Rebels on these front lines are the Free Syrians who come from these villages and have no other place to go to," said one fighter who asked that his name not be used, for safety reasons.
"We are not foreigners who can easily leave," he added, contrasting his unit to the Nusra Front and the Islamic State, which have attracted foreign fighters. "We belong here, and our families and land are here."
Syrian government troops advanced on Monday toward a crucial highway held by insurgents, taking several villages in Hama province with the help of Russian airstrikes, according to Syrian and Russian state news media, antigovernment activists and fighters.
A senior commander of Hezbollah, the Lebanese Shiite militia group that has been battling alongside Assad's forces, was killed on Sunday in the fighting. He was identified as Hassan Mohammad Hussein al-Hajj by Hezbollah news outlets, which provided live coverage of his funeral Monday.
Videos from the battlefield in recent days showed Russian attack helicopters swooping low over fields, seemingly close enough to touch, then veering upward to fire barrages of rockets, flares and heavy machine-gun fire.
Warplanes dropped leaflets over Idlib and Latakia, farther north, trying to persuade insurgents to surrender.
"40 types of ammunition … are waiting for you," one read. "Able to destroy targets (ground-underground-shelters and fortified areas)."
Another read: "O Gunman: It is time for the truth. The world is changing rapidly. The army is coming. Think of yourself." It added, "Drop your weapon to keep your life and future."
Insurgents and antigovernment activists conducted their own information campaign, circulating videos showing how to disarm what they said were Russian cluster bombs and listing helpful Russian military terms that might be overheard on radio transmissions.
Maher Samaan and Hwaida Saad contributed reporting from Beirut, and Karam Shoumali from Istanbul.