BEIRUT — Backed by Russian aircraft, Syrian troops pushed Friday toward the historic central town of Palmyra in an offensive to recapture it from the Islamic State group whose fighters have damaged some of the world's most precious archaeological sites since they overran the town last May.

After night fell, Syria's state news agency SANA reported that the offensive advanced toward Palmyra and that scores of Islamic State fighters have been killed or wounded in Syrian artillery fire near the town.

Activists who monitor the Syrian conflict reported intense airstrikes in Palmyra and its suburbs.

In Moscow, a Russian Defense Ministry official confirmed his country's warplanes in Syria were flying in support of the Syrian offensive.

Lt. Gen. Sergei Rudskoi said Russian aircraft were conducting 20-25 sorties a day in support of the Palmyra offensive, even though Russia this week drew down its military presence in Syria after President Vladimir Putin ordered a partial pullout from Syria, in support of the Geneva peace talks.

The U.N.-brokered talks between representatives of the Syrian government and the Western-backed opposition adjourned for the weekend after five days of proximity discussions.

Though Rudskoi's statements indicated that Russian aircraft supporting the Palmyra offensive were carrying out airstrikes, U.S. military officials raised doubts, saying the Russians have conducted no airstrikes in the last several days but that the Syrian regime has done so.

U.S. Air Force Col. Pat Ryder said the U.S. military has seen the Russians launching artillery strikes instead.

“We assess that those strikes near Palmyra and elsewhere were from Russian artillery,” Ryder said.

If the Syrian army and its allies capture Palmyra, in the central province of Homs, it would be a major victory against the militants in Syria.

“If the regime keeps the current momentum of its offensive, they can take Palmyra within days,” said Turkey-based activist Osama al-Khatib, originally from Palmyra.

The Islamic State has built strong defenses in the town, including trenches around it, taking advantage of a sandstorm earlier this week to launch counterattacks, said al-Khatib, speaking over the phone.

He said Syrian government forces were now about six miles from the town.

According to two activist groups, the Britain-based Syrian Observatory for Human Rights and the Local Coordination Committees, warplanes conducted more than a dozen airstrikes since Friday morning.

The Observatory said troops were slowly advancing toward Palmyra, adding that both sides were bringing in reinforcements. It said there were casualties on both sides.

Syrian troops and their allies have been on the offensive in the area since last week.

A television channel belonging to Lebanon's Hezbollah group, which is allied with Syrian President Bashar Assad, said Syrian troops captured another hill just northwest of Palmyra on Friday.

In Geneva on Friday, Bashar Ja'afari, the head of the government team and Syria's U.N. ambassador, said the latest round of talks with the U.N. special envoy Staffan de Mistura was “useful” and focused on “fundamental principles” for a solution to the Syrian conflict that his side had presented.

Later in the day, the head of the Syrian opposition delegation, Asaad al-Zoubi, said his side is focused on achieving a “transitional governing body with full executive powers” for Syria.

De Mistura said an upcoming meeting between U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov could be “crucial” to help move toward a political transition in the country after five years of war.

Kerry is expected in Moscow next week.