Syrian Military Says US-Russian Brokered Cease-Fire Over

— -- A Syrian human rights group said today that at least 32 people had been killed and dozens injured in Aleppo, Syria, and its western suburbs in the hours after Syria's military declared the U.S.-Russian brokered cease-fire over.

After the Syrian military blamed rebels for not observing the truce, which was in its seventh day, the United Nations said a convoy transporting aid to the hard-hit city had been attacked, with 18 of the convoy's 31 trucks initially believed to have been hit.

The rights group, the Syrian Observatory for Human Rights, said that 12 people had been killed when the convoy was struck. Farhan Haq, a deputy spokesman for U.N. Secretary-General Ban Ki-moon, told ABC News that he could not confirm any information on potential casualties or the cause of the attack. He said that the United Nations' initial understanding was that a warehouse operated by the Syrian Arab Red Crescent had also been hit along with the convoy, before the trucks could distribute any aid to 78,000 people whom international groups had hoped to reach.

The fighting came amid signs the cease-fire was falling apart, with Russia casting doubt on it and the Syrian military declaring its conclusion.

But U.S. Secretary of State John Kerry, speaking to reporters in New York City, disputed the notion that the cease-fire had ended and redirected his frustrations toward the Russians.

"We have not had seven days of calm and delivery of humanitarian goods, and so it'd be good if they didn't talk first to the press but if they talked to the people who are actually negotiating this," Kerry said. "And I think it's -- as I said yesterday -- time to end the grandstanding and time to do the real work of delivering on the humanitarian goods that are necessary for access. So we just began today to see real movement of humanitarian goods, and let's see where we are, and we're happy to have a good conversation with them about how to proceed."

Kerry is in New York City for the United Nations General Assembly, where international leaders will discuss the world's refugee crisis in a large part caused by the five-year Syrian war.

In a statement, State Department spokesman John Kirby stressed that the U.S. was waiting to hear from Russia on the current state of the cease-fire.

"While we have seen comments attributed to the Syrian military, our arrangement is with Russia, which is responsible for the Syrian regime's compliance, so we expect Russia to clarify their position," he said.

Before today's declaration by the Syrian military, the cease-fire was already on shaky ground, with reports of violations on both sides.

According to the Syrian Observatory for Human Rights, the besieged city of Aleppo was hit by at least four airstrikes on Sunday. The group also reported that convoys carrying humanitarian aid shipments had not received permission to enter the city, which desperately needs them. Aleppo is home to nearly 2 million people who lack regular access to water and electricity. An estimated 250,000 to 275,000 people live in areas held by anti-government rebels that have been a focus of intense airstrikes and artillery bombardment.

Additionally, on Saturday the U.S.-led coalition fighting ISIS halted an airstrike in eastern Syria that the Russian Defense Ministry said killed 62 Syrian government soldiers and injured 100 others.

A U.S. defense official told ABC News that the strike was supposed to target a collection of vehicles and personnel believed to belong to ISIS. The airstrike was halted after Russia communicated to the coalition that it was Syrian forces that were being struck. Australia, Denmark and the United Kingdom have acknowledged that their aircraft participated in the strike.

A senior Obama administration official told ABC News that the U.S. "relayed our regret" to the Syrian government through Russian officials.

According to a U.S. defense official, the leading theory is that the Syrian forces hit in the airstrike may have been conscripts or prisoners wearing civilian clothes, not regular Syrian Army uniforms.

The cease-fire must be renewed every 48 hours. The last extension was on Friday.

ABC News' Luis Martinez contributed to this report.