Yet another Iranian Revolutionary Guards commander has been killed fighting in Syria Thursday, as Tehran ups its direct military intervention to prop up the increasingly desperate regime of Bashar al-Assad.

Syrian rebel sources first reported Iranian Akil Bakhtiyari had been killed in fighting in the Qalamoun region bordering Lebanon, where a pro-regime operation led by Hezbollah is seeking to root-out strategically-important rebel strongholds.

Bakhtiyari’s death was confirmed by numerous Iranian media sources, including the state-controlled Press TV.

He is the second officer in the elite Revolutionary Guards to have been confirmed dead this week, after commander Jassem Nouri was reportedly killed fighting in neighboring Iraq.

Iran has invested heavily in both Syria and Iraq to secure its regional allies and proxies in the face of rebellions by Sunni rivals. In both countries, that aid has included arming and equipping pro-regime militias, as well as sending direct help in the form of Hezbollah and Iranian fighters.

The latest Iranian casualty in Syria comes one day after a Syrian official said Tehran would be sending thousands more fighters to secure Syria’s capital Damascus from advancing rebel armies.