A civil defence member carries an injured girl after an airstrike in the rebel-controlled city of Idlib, Syria. Image Credit: Reuters

Beirut: At least 80 Syrian soldiers were killed in a US air strike at an army position near Deir Al-Zour airport on Saturday, the Syrian Observatory for Human Rights, a Britain-based monitoring group said, citing a source at the airport.

The Syrian state media said the raid was carried out at 5:00pm local time (1400 GMT, 6pm UAE).

The Pentagon on Saturday said that their  forces may have conducted an air strike on Syrian military position.  The U.S. military said they had halted an air strike south of Deir Al Zour, Syria, on Saturday after Russian officials said the targeted personnel and vehicles may have been part of the Syrian military.

The strike was in an area the US had attacked in the past, and US-led coalition members had informed their Russian counterparts before it began, the U.S. military's Central Command said in a statement.

It was issued after Russia and a war monitoring group said U.S.-led coalition jets bombed a Syrian army position near Deir Al-Zour airport on Saturday.

Russian jets had been bombing in the same area at the same time, the Observatory said.

The source at the airport said the air strike had paved the way for Daesh fighters to overun the position at Jebel Tharda, the Observatory said.

It said earlier that only 30 soldiers had been killed, citing the same source.

Earlier on Saturday, a Russian Defense Ministry spokesman, said that 62 Syrian soldiers have been reported killed in a US airstrikes on a military base.

Maj. Gen. Igor Konashenkov says the airstrike on Saturday took place near the Deir Al-Zour airport in eastern Syria and was carried out by two F-16s and two A-10s.

He did not identify the planes’ country affiliation, but said they were part of the international coalition.

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Konashenkov says Syrian authorities told the Russians that more than 100 soldiers were wounded. He says the planes came from the direction of the border with Iraq.

Russia is a key ally of Syrian President Bashar Assad’s government and has been carrying out airstrikes on behalf of his forces since last year.

Russia and the United States brokered a cease-fire in Syria that took effect on Monday and has largely held despite dozens of alleged violations.

Shaky ceasefire  

Earlier on Saturday,  Russia and Syrian rebels cast doubt over the prospects for an increasingly shaky five-day-old ceasefire, with Moscow saying the situation was worsening and a senior insurgent warning that the truce "will not hold out".

The ceasefire is the result of an agreement between Russia, which backs Syrian President Bashar Al-Assad with air power, and the United States, which supports some rebel groups.

It has reduced the fighting since coming into effect on Monday.

Aid blocked

However, some violence has persisted across Syria, and promised aid deliveries to besieged areas remain blocked, with both sides accusing the other of bad faith.

Russia's Defence Ministry said conditions in Syria were deteriorating, adding that it believed the ceasefire had been breached 199 times by rebels and saying the United States would be responsible if it were to collapse.

Earlier on Saturday, Russian President Vladimir Putin cast doubt over Washington's commitment to the deal, but also said he believed that securing a ceasefire was a common goal for the two countries, which both agreed to extend it on Friday.

Insurgents say they only reluctantly accepted the initial deal, which they believe is skewed against them, because it could relieve the dire humanitarian situation in besieged areas they control, and blamed Russia for undermining the truce.

"The truce, as we have warned, and we told the (U.S.) State Department — will not hold out," the rebel official said, pointing to the continued presence of a U.N. aid convoy at the Turkish border awaiting permission to travel to Aleppo.

"It is not possible for the party (Russia) that wages war against a people to strive to achieve a truce, as it is also not possible for it to be a sponsor of this agreement while it bombs night and day, while on the other side, the other party — America — has the role of spectator," he said.

Moscow has itself accused rebels of breaking the truce and said Washington needs to do more to make them abide by its terms, including separating from the jihadist Jabhat Fateh al-Sham, which only broke formal allegiance to al Qaeda in July.

The five-year-old civil war has killed hundreds of thousands and displaced half the country's population, drawing in global and regional powers, causing an international refugee crisis and inspiring jihadist attacks around the world.

Overnmighit shelling

Both sides have accused the other of being responsible for aid deliveries being stuck far from Aleppo, where army and rebel forces were supposed to pull back from the Castello Road which leads into besieged, insurgent-held eastern districts.

Russia on Friday said the Syrian army had initially withdrawn but returned to its positions after being fired on by rebels, who in turn say they saw no sign of government forces ever leaving their positions.

"There is no change," said Zakariya Malahifji, an official for a rebel group in Aleppo on Saturday, asked whether there had been any move by the army to withdraw from positions along the road.

Syria's government said it was doing all that was necessary for the arrival of aid to those in need it in all parts of the country, particularly to eastern Aleppo.

Two convoys of aid for Aleppo have been waiting at the Turkish border for days. The U.N. has said both sides in the war are to blame for the delay of aid to Aleppo, where neither has yet withdrawn from the Castello Road into the city.

But senior U.N. officials have accused the government of not providing letters to allow convoys to reach besieged areas in Syria. The government said the road was being fired on by rebels, which they deny, so it could not give convoys a guarantee of safety.

Warplanes strafed or bombed rebel-held areas in the northwestern province of Idlib, as well as positions north of the city of Homs and east of the city of Hama overnight, the Syrian Observatory for Human Rights said.