Air strikes hit around 20 aid trucks outside a Red Crescent center in the Syrian province of Aleppo on Monday, a monitor said, hours after the army declared a week-long truce to be over.

The Britain-based Syrian Observatory for Human Rights did not immediately report any casualties in the raids on the Orum al-Kubra area, west of Aleppo city.

United Nations spokesman Stephane Dujarric said: “We understand a convoy has been hit. We are trying to get more information.”

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The strikes came shortly after Syria’s army declared an end to the ceasefire between the regime and non-jihadist rebels brokered by Russia and the United States.

David Swanson, a spokesman for the UN Office for the Coordination of Humanitarian Affairs, said earlier Monday that a convoy on trucks was crossing into Orum al-Kubra with “wheat flour, health supplies and other emergency supplies” for 78,000 people in the area.

Observatory head Rami Abdel Rahman said the trucks arrived in the afternoon.

More than 300,000 people have been killed and millions displaced since the Syria conflict started in 2011 with anti-government protests.

The State Department said it was prepared to extend the ceasefire window in the hopes that if it held, the US and Russia could then turn to their planned military cooperation against the Islamic State militants and al-Qaeda-linked groups in Syria.

The latest developments placed added importance on 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 Kerry and Russian Foreign Minister Sergey Lavrov.

“Well, the Syrians didn’t make the deal,” Kerry told reporters in New York on Monday. “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.”

State Department spokesman John Kirby said the US is ready to work with Russia to strengthen the terms of the ceasefire 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 US-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.