Meeting with a senior Iranian official in Damascus, Assad highlighted "important gains by the Syrian army in the fight against terrorism, with the support of its friends led by Iran and Russia," state news agency SANA reported.
But these gains, he said, have "pushed certain countries hostile to Syria and who pretend to fight terrorism to... increase their financing and arming of terrorist groups."
Since the outbreak of Syria's conflict in 2011 Assad has accused Sunni Muslim countries including Turkey and Gulf nations of arming his mainly Sunni opponents.
Iran, the region's main Shiite power, has also backed Assad, including with the reported deployment of hundreds of "military advisers" to bolster regime forces.
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After his talks with Assad, Ali Akbar Velayati, a top adviser to Iran's supreme leader, said Tehran was determined to "continue its support for the Syrian government and people, because the war against terrorism is crucial for the region and the world."
Velayati also praised Iran for its "exceptional resistance" to "terrorists supported by regional and Western countries".
"This is the real prelude to the success of any political solution decided by Syrians," he said.
Assad routinely denounces all armed opponents of his regime as "terrorists" regardless of their motives or affiliation.
Syria's conflict broke out in March 2011 initially as an anti-regime uprising but evolved into a multi-front war that sees the regime, jihadists including the Islamic State group, secular rebel forces and a range of ethnic militias battling for territory.
More than 250,000 people have died in the fighting and millions have been forced from their homes.