The European Union is set to slap fresh sanctions on President Bashar al-Assad's regime on Monday, targeting six entities and clarifying an existing arms embargo, EU diplomatic sources said.

The measures were agreed by ambassadors of the 27-nation-bloc early Monday and will be approved later in the day by EU foreign ministers meeting in Luxembourg.

The asset freeze and travel against the six entities, some of them government ministries, according to the sources, will be the 16th round of restrictive EU measures against the Assad regime.

They will include clarification of the rules on insuring items embargoed for delivery to Syria, stating in black and white that insuring arms deliveries to Syria is banned under an arms embargo decided last year.

The measure follows an incident some days ago involving a British-insured Russian cargo ship, allegedly carrying attack helicopters for Syria.

The United States alerted Britain to the consignment and British security services told insurers Standard Club that providing insurance for the shipment would breach EU sanctions, reports said.

Standard Club then cancelled insurance for the ship as well as others in the fleet owned by Russian cargo line Femco, forcing the vessel to head home.