MOSCOW/BEIRUT: Moscow stepped up its war of words with Washington Sunday, saying airstrikes by a U.S.-led coalition on the Syrian army threatened the implementation of a U.S.-Russian cessation of hostilities plan for Syria and bordered on connivance with Daesh (ISIS). The diplomatic row heated up on the last day of a seven-day cessation of hostilities marred by a surge of violence as warplanes hit the strategic northern city of Aleppo for the first time since the truce came into effect.

The Russian Defense Ministry said Saturday that U.S. jets had killed more than 60 Syrian soldiers in the eastern Syrian city of Deir al-Zor in four airstrikes by two F-16 and two A-10 fighter jets coming from the direction of Iraq.

Syria’s U.N. Ambassador Bashar Jaafari charged that U.S.-led strikes were aimed at torpedoing the cessation deal, but France’s foreign minister, speaking in New York, placed the main blame for truce violations on the government of President Bashar Assad.

The Britain-based Syrian Observatory for Human Rights cited a military source at Deir al-Zor airport as saying at least 90 Syrian soldiers had been killed in the four airstrikes. Russia’s Foreign Ministry denounced the U.S. position on the incident as “unconstructive and inarticulate.”

“The actions of coalition pilots – if they, as we hope, were not taken on an order from Washington – are on the boundary between criminal negligence and connivance with [Daesh] terrorists,” it said in a strongly worded statement. “We strongly urge Washington to exert the needed pressure on the illegal armed groups under its patronage to implement the cease-fire plan unconditionally. Otherwise the implementation of the entire package of the U.S.-Russian accords reached in Geneva on Sept. 9 may be jeopardized.”

Russia has called on the United States to press units of the moderate Syrian opposition to separate themselves from Daesh and other “terrorist groups.”

Iran also condemned the U.S. military action. “Such moves indicate America supports terrorist groups in Syria,” a Foreign Ministry spokesman said, according to Iranian news agencies.

But French Foreign Minister Jean-Marc Ayrault said that despite the U.S.-led coalition airstrikes on the Syrian army, it was Syrian government forces which were principally behind the truce violations.

“We have to hold on to this accord and keep it alive at all costs so we need to get over the events of the last few hours,” Ayrault told reporters. “But while there were these incidents ... we shouldn’t forget that what has harmed the American-Russian cease-fire is firstly the regime. It is always the regime of Bashar Assad.”

The U.S. military said the coalition stopped the attacks against what it believed to be Daesh positions in northeast Syria after Russia informed it that Syrian military personnel and vehicles may have been hit.

“The White House is defending [Daesh]. Now there can be no doubts about that,” Russian Foreign Ministry spokeswoman Maria Zakharova said in comments aired by state TV.

The U.S. Ambassador to the United Nations, Samantha Power, said Zakharova should be embarrassed by that claim. Russia’s U.N. representative Vitaly Churkin said Russia had no “specific evidence” of the U.S. colluding with Daesh militants.

The diplomatic row should further complicate humanitarian aid deliveries to Syria, including its largest prewar city Aleppo where the fragile truce is under threat.

Aleppo was hit by airstrikes for the first time since the truce began, killing a woman and wounding others. Moscow said militants there were preparing for large-scale military actions against Syria’s army.

An AFP correspondent in Aleppo’s Karm al-Jabal district saw several wounded children after a raid.

Heavy clashes continued Sunday east of Damascus in the rebel-held Jobar suburb, the Observatory and a witness said.

The Al-Rahman Legion, part of a Free Syrian Army rebel alliance there, said its fighters had destroyed a government tank and killed soldiers after government forces tried to storm Jobar for the second time this week.

The Observatory said at least eight people died and many were seriously injured when helicopters dropped barrel bombs onto a town in a rebel-held part of the southern Syrian province of Deraa Sunday.

Rebels say they only reluctantly accepted the initial deal to relieve the dire humanitarian situation in besieged areas they control, and blamed Russia for undermining the truce.

“The truce ... will not hold out,” a senior rebel official in Aleppo said.

Rebels have also accused Russia of using the cessation of hostilities to give the Syrian army and allied forces a chance to regroup and deploy forces ready for their own offensives.

Daesh is excluded from the deal. Separate U.S.-led, Damascus-led and Turkey-backed operations against the militants have continued throughout the cessation of hostilities on various fronts, such as the Syrian border town of Al-Rai.

Also Sunday, Daesh said it had shot down a warplane in Deir al-Zor with “anti-aircraft” guns, in the same area as the U.S.-led coalition strikes hit the Syrian military Saturday. The Syrian military confirmed the loss of a warplane it said was carrying out an operation against rebels.