Assad's days-long trip to China will mark one of his longest spells of absence in Syria since his country's civil war broke out.

After an earthquake killed more than 50,000 people in Turkey and Syria, Syria allowed the UN to use those two border crossings from Turkey to dispatch aid.

Like other countries around the Mediterranean, Syria has been hit hard by wildfires this month, supercharged by strong winds and searing temperatures.

Accreditation of the BBC Radio correspondent in Syria has also been revoked.

UN investigators in 2012 concluded there were reasonable grounds to believe shabbiha militias committed crimes against humanity, including murder and torture, and war crimes.

With the war far from over and Assad still internationally isolated, analysts say sanctions will likely continue to deter investment.

Tehran has been a key ally to Damascus throughout Syria's war, offering vital economic and military assistance that has helped the Syrian government claw back most of the territory it lost at the start of the conflict.

The visit comes just weeks after Iran's landmark agreement to restore ties with regional rival Saudi Arabia and amid a flurry of diplomacy in the Middle East as regional relations with Iran and Syria shift.

It says the raid targeted Abd-al-Hadi Mahmud al-Haji Ali and was initiated after gathering intelligence that Islamic State was plotting to kidnap officials abroad.

Any recommendation to reinstate Syria to the 22-member Arab League, whose next meeting is due to be held in Saudi Arabia next month, is likely to draw protests from Western capitals.

With Iran's president also expected in Saudi soon, and the Saudis negotiating with Yemen's Huthi rebels this week in an attempt to end fighting there, optimism has blossomed for the turbulent Gulf region.

Israel has for several years been mounting attacks on what it has described as Iran-linked targets in Syria.