Beirut: IS militants killed 26 Syrian soldiers on Monday west of Palmyra, a monitoring group said, after days of advances by government forces backed by Syrian and Russian air cover.
Russian President Vladimir Putin said last week that the Syrian army would soon recapture Palmyra from IS, which has held the desert city for nearly a year.
Palmyra has both symbolic and military value as the site of ancient Roman-era ruins - mostly destroyed by the ultra-hardline group - and because of its location on a highway linking mainly government-held western Syria to IS's eastern stronghold.
The Britain-based Syrian Observatory for Human Rights said the fighting took place about 4 km (2 miles) west of Palmyra.
It was not possible to independently verify the death toll. Syria's state news agency SANA said the army and allied forces, backed by the Syrian air force, carried out "concentrated operations" against IS around Palmyra and the IS-held town of Al Qaryatayn, about 100km further west.
After more than five months of air strikes in support of Syrian President Bashar Al Assad, Putin announced the withdrawal last week of most Russian forces.
But Russian planes have continued to support army operations near Palmyra, according to the Observatory and regional media, and Putin said on Thursday he hoped that the city would soon fall to the Syrian government.
"I hope that this pearl of world civilisation, or at least what's left of it after bandits have held sway there, will be returned to the Syrian people and the entire world," he said.
In southern Syria, a militant group loyal to IS seized a village near the Jordanian border and the Israeli-occupied Golan Heights on Monday from Al Qaeda's Syrian affiliate, the Nusra Front, the Observatory said.
It said the Yarmouk Martyrs' Brigade captured the village of Tasil, about 10 km (6 miles) from the Golan Heights and a similar distance from the Jordanian border.
Abu Saleh Al Musalima, Nusra Front commander in the south of the country, was killed in the fighting, the Observatory said, as well as three insurgents from other factions fighting alongside the group, Al Qaeda's Syrian affiliate.
IS and the Nusra Front are both excluded from an internationally backed limited truce in Syria, which has been in place for nearly three weeks to allow peace talks to take place in Geneva between the government and opposition groups.
Meanwhile, Russia will act unilaterally against those militants who violate ceasefire in Syria if Moscow does not reach agreement with the United States on a mechanism of detecting and preventing truce breaches, Russia's Foreign Ministry said on Monday.
The ceasefire agreement, worked out by Russia and the US, is largely respected, the ministry said.
But the two nations, which co-chair the Syria International Support Group, have so far failed to agree on terms of preventing all cases of ceasefire violations, which sends a wrong signal to "those members of the opposition... who have not dissociated themselves clearly enough from well-known terrorist groups", it said.
Russia's general staff of the armed forces proposed earlier on Monday to hold an urgent meeting with US representatives to agree on the mechanism of controlling the ceasefire in Syria, saying it would act unilaterally starting from March 22 if it gets no response.
The United States later rejected the call from Russia's military, saying that its concerns were already being handled in a constructive manner.