WASHINGTON An attack on a convoy carrying humanitarian supplies in the Aleppo area of Syria appeared to be an air strike but it was not carried out by coalition jets, U.S. Central Command spokesman Colonel John Thomas said on Tuesday.
"It was certainly not the coalition who struck from the air. It does look like an air strike," Thomas told reporters during a telephone briefing.
"The only other entities that fly in Syria are Russia and Syria," he said.
The incident could deal a powerful blow to the ceasefire, the latest attempt to halt a war in its sixth year.
The Syrian Red Crescent said the head of one of its local offices and "around 20 civilians" were killed in Monday's strike, which the Syrian Observatory for Human Rights blamed on Russian or Syrian aircraft.
Russia, which is allied with Syria's President Bashar al-Assad's government, denied that either its air force or the Syrian armed forces was responsible. The Syrian army also denied that it was involved in the attack.
The United Nations suspended aid shipments into Syria on Tuesday.
Thomas said the ceasefire in Syria was in jeopardy because of increased violence.
"This is not the vision that I think was put in place more than seven days ago, to try to get humanitarian assistance flowing into the area and try to decrease the level of violence," Thomas said.
On Saturday, Russia said that U.S. jets had killed more than 60 Syrian soldiers.
The strike triggered a war of words between Washington and Moscow and further strained the cessation of hostilities.
Thomas said a brigadier general would be appointed to investigate the incident.
(Reporting by Idrees Ali; Editing by Diane Craft)