BEIRUT—A senior commander of Iran's elite Revolutionary Guard Corps, Gen. Hassan Shateri, was assassinated on Tuesday, Iranian news agencies said.

Gen. Shateri was killed outside Iran by "Zionist agents," according to some Iranian news agencies. Iranian news site Balagh and a person with knowledge of the situation said he was killed in Syria, making him the highest-ranking Iranian official killed in Syria's uprising.

He was a senior commander in the Quds Forces, the IRGC unit that serves outside Iran's borders training proxy militia and safeguarding the Islamic Republic's interests in places like Lebanon, Iraq and Afghanistan, according to the person with knowledge of the situation.

Gen. Shateri headed Iran's efforts to help southern Lebanon rebuild after the 2006 war with Israel, according to Iranian media, which said he had arrived in Beirut immediately after the conflict. In Lebanon, Gen. Shateri worked under the alias Husam Khoshnevis, according to Iranian and Lebanese media, which have quoted Gen. Shateri and published his picture under that name in articles discussing rebuilding activities, suggesting he was hiding his military background while serving in a civilian role.

The Iranian Embassy in Beirut said in a statement Wednesday night that Husam Khoshnevis, the head of Iran's reconstruction project in southern Beirut, had been assassinated by armed terrorists on his way from Damascus to Beirut.