UN Secretary-General Ban Ki-moon has appealed for restraint to avoid an escalation in Syria's civil war, expressing "grave concern" over Israeli air raids.

Israel launched air strikes earlier that hit three military sites near Damascus, the second such reported attack in a 48-hour period targeting the transfer of arms to Lebanon-based Hezbollah, raising fresh concerns of a regional spillover.

"The secretary-general calls on all sides to exercise maximum calm and restraint, and to act with a sense of responsibility to prevent an escalation of what is already a devastating and highly dangerous conflict," Ban's spokesman Martin Nesirky said in a statement on Sunday.

Nesirky said the United Nations was unable to independently verify the raids, and had no details about them, but Ban "expresses grave concern over reports of air strikes in Syria by the Israeli Air Force."

"The secretary-general urges respect for national sovereignty and territorial integrity of all countries in the region, and adherence to all relevant Security Council resolutions," Nesirky said.

Ban spoke by telephone with Arab League chief Nabil al-Arabi about the reports, which have triggered fears of further escalation in a conflict that has already killed more than 70,000 people in just over two years.

The two men "shared their grave concern about the reported air strikes in Syria and the risks for regional security," Nesirky said.

UN Deputy Secretary-General Jan Eliasson is set to purse the talks on the sidelines of the Somalia conference in London on Tuesday.