GENEVA/BEIRUT (Reuters) - The fate of President Bashar al-Assad will play no part in talks to end the Syrian war, the head of the government’s delegation said, leading the U.N. peace envoy to warn that lack of progress on the issue could threaten a fragile cessation of hostilities.

Damascus delegate Bashar Ja’afari said Assad’s future had “nothing to do” with the negotiations, which entered their second week on Monday, insisting that counter-terrorism efforts remained the priority for the government.

“The (terms of) reference of our talks do not give any indication whatsoever with regard to the issue of the President of the Syrian Arab Republic,” he said when asked about the willingness of the government delegation to engage in serious talks on political transition.

“This is something already excluded.”

U.N. envoy Staffan de Mistura - who describes Syria’s political transition as “the mother of all issues” - responded by saying the government delegation’s refusal to discuss it could lead to a deterioration of the situation on the ground.

“Everyone more or less agrees, the cessation of hostilities is still holding,” he said. “The same ... more or less for the movement on humanitarian aid. But neither of them can be sustained if we don’t get progress on the political transition.”

The fragility of the three-week-old cessation, which was backed by the United States and Russia, was highlighted on Monday when Moscow said it had recorded six violations in the last 24 hours.

The Syrian opposition accused the government delegation of wasting time by refusing to discuss the future of Assad. “It is not possible to wait like this, while the regime delegation wastes time without achieving anything,” said Salim al-Muslat, spokesman for the opposition High Negotiations Committee.

Syria's President Bashar al-Assad speaks during an interview with Spanish newspaper El Pais in Damascus, in this handout picture provided by SANA on February 20, 2016. Picture taken February 20, 2016. REUTERS/SANA/Handout via Reuters

DESERT CITY

Arguments over Assad’s fate were a major cause of the failure of previous U.N. peace efforts in 2012 and 2014 to end a civil war that has killed more than 250,000 people and caused a refugee crisis.

The five-year-old conflict between the government and insurgents has also allowed Islamic State to take advantage of the chaos and take control of areas in the east of the country.

Fighters from the jihadist group - which is excluded from the ceasefire deal - 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 Islamic State, 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 Islamic State - and because of its location on a highway linking mainly government-held western Syria to Islamic State’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 Islamic State around Palmyra and the Islamic State-held town of al-Qaryatayn, about 100 km further west.

After more than five months of air strikes in support of Assad, which turned the course of the civil war in the government’s favour, 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.