Syrian President Bashar al-Assad in a recent message to Iran's Supreme Leader Ayatollah Seyyed Ali Khamenei has thanked the country for its role in lifting the siege of Deir ez-Zor city, an Islamic State stronghold in eastern Syria, IRNA reports.

The Iranian people have always stood by Syria in the fight against terrorism, President Assad said in the letter.

"We share our victory with the Iranian people who also sacrifice their blood to stop terrorists," said the Syrian president.

"The Syrian Arab Republic and the Islamic Republic of Iran are to continue their fight against injustice, aggressions and terrorism threats, he said in his message to Ayatollah Khamenei.