At least 54 people were killed and dozens wounded when an air strike hit a fuel station in Syria's northern province of al-Raqqa on Thursday, the Syrian Observatory for Human Rights said.
The British-based group, which has a network of activists across Syria, cited an activist in the region saying that more than 110 people were among the dead and wounded.
The deaths came as Iraq denied a Western intelligence report that said Iranian aircraft had flown weapons and military personnel over Iraqi airspace to Syria to help President Bashar al-Assad battle the 18-month-old uprising. The allegation said arms transfers were organised by the Islamic Revolutionary Guard Corps.
Although charges that Iraq has allowed Iran to send arms to Syria are not new, the report said the extent of such shipments is far greater and more systematic than has been publicly acknowledged, thanks to a deal between senior Iraqi and Iranian officials. The report also said Iran was dispatching trucks overland via Iraq to Syria.
"Iraq has confirmed that it will never be involved in helping or allowing any shipment via its air space or land to Syria," Iraqi government spokesman Ali al-Dabbagh said. He added Iraq was "ready to be part of regional and international efforts or measures to stop the shipping of equipment or personnel to both sides in Syria".Reuse content