According to the Lebanese Foundation for Peace:
Missing Israeli Soldiers Held at the Iranian Embassy in Beirut
Delicate Intelligence information coming out of Hezbollah indicated that the 2 missing captives of the Israeli Army Ehud Goldwasser and Eldad Regev have been smuggled outside Southern Lebanon to the capital.
They are secretly being held at the Embassy of Iran in Beirut, under direct Iranian security guards supervision.
Hat tip: Israel Matzav (who can’t verify the report).