Iraqi forces in the past pounded IS positions inside Syria after getting the green light from Syrian authorities (Photo: Reuters)

The development comes as the two neighbors, who are also both allied with Iran, work to coordinate their fight against rival groups ahead of a planned US military withdrawal from Syria.

Iraqi warplanes and artillery have pounded IS positions inside Syria in the past, after getting the green light from Syrian authorities. On Saturday, al-Assad received a letter from Iraq's Prime Minister Abdul-Mahdi calling for both countries' coordination in fighting terrorism.