The United States is demanding that Russia live up to its commitments in Syria's fractured week-old truce, after the Syrian military announced it was over amid numerous violations including an attack on an aid convoy and apparent Russian unwillingness to press Damascus on the point.

The latest developments lent more urgency to a meeting Tuesday of the International Syria Support Group, or ISSG, which is comprised of countries with a stake in the conflict and endorsed the truce, to be led by Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov. Kerry called the convoy attack an "egregious violation" of the cease-fire and said the U.S. "will reassess the future prospects for cooperation with Russia."

"The destination of this convoy was known to the Syrian regime and the Russian federation and yet these aid workers were killed in their attempt to provide relief to the Syrian people," State Department spokesman John Kirby said in a statement Monday night.

Despite the setback, the State Department said it was prepared to extend the cease-fire window in the hopes that if it held, the U.S. and Russia could then turn to their planned military cooperation against the Islamic State militants and al-Qaida-linked groups in Syria.

"Well, the Syrians didn't make the deal," Kerry told reporters in New York. "The Russians made the agreement. So we need to see what the Russians say; but the point, the important thing is, the Russians need to control (Syrian President Bashar) Assad, who evidently is indiscriminately bombing, including of humanitarian convoys. So let's wait and see, collect the facts. We need to see where we are, and then we'll make a judgment. But we don't have all the facts at this point."

An official with the Syrian Red Crescent said aid trucks operated by the group and destined for a rebel-held area in Aleppo province had been hit by an airstrike, as warplanes resumed their bombings in Aleppo province.

Kirby said the U.S. is ready to work with Russia to strengthen the terms of the cease-fire agreement and expand deliveries of humanitarian aid. But he added that Russia must clarify its position on the status of the truce.

Russia took the side of the Syrian government, blaming the rebels for violating the truce. Russia's Foreign Ministry said the failure of Syrian rebels to adhere to the truce "threatens the cease-fire and U.S.-Russian agreements."

The ministry statement came after the Russian military said that continuing rebel violations made it "meaningless" for the Syrian army to respect the deal. The Syrian military said earlier Monday that the cease-fire had expired.

Kirby noted that the cease-fire arrangement was agreed to by the United States and Russia, which is responsible for the compliance of the Assad government.

"We are prepared to extend the cessation of hostilities, while working to strengthen it and expand deliveries of assistance," Kirby's statement said. "We will be consulting with our Russian counterparts to continue to urge them to use their influence on Assad to these ends."

While acknowledging numerous violations, Kirby said the truce, which took effect last Monday, had been responsible for "a measure of reduced violence." However, he also repeated calls for the sustained delivery of humanitarian aid to Aleppo and other besieged communities. Such deliveries began only on Monday and were available only in limited areas, he said.

France's foreign minister criticized both the United States and Russia for the cease-fire pact that excluded the international community, saying it must have wide support if it's going to be implemented. However, the U.S. officials said details of the agreement were shared on Monday.

Saudi Foreign Minister Adel al-Jubeir pledged his country's support for Syria's opposition forces, along with representatives of Qatar, Turkey and European nations, and stressed that Assad cannot remain in power, even though that issue has been delayed until the fighting wanes.

Kerry expressed frustration with the touch-and-go cease-fire. "We have not had seven days of calm and of delivery of humanitarian goods," Kerry said. Those seven days of calm and aid deliveries were required before the U.S. and Russia could embark on a plan to cooperate in targeting the Islamic State group and al-Qaida affiliates working in Syria.

The Syrian military said in a statement Monday that "armed terrorist groups" repeatedly violated the cease-fire and took advantage of the truce to mobilize and arm themselves while attacking government-held areas. The statement said the rebels wasted a "real chance" to stop the bloodshed.

A Syrian activist group said 92 people have been killed in Syria since the start of the cease-fire. The Britain-based Syrian Observatory for Human Rights said 29 children and teenagers were among those killed, as well as 17 women. The figure does not include dozens of Syrian soldiers and Islamic State militants killed in the eastern province of Deir el-Zour, the Observatory said Monday.

A mistaken air raid by the U.S.-led coalition also killed 62 Syrian soldiers.

The opposition reported 254 violations by government forces and their allies since the truce started on Sept. 12, and a senior Syrian opposition official declared the cease-fire "clinically dead."

Syrian state media said there were 32 violations by rebels on Sunday alone.