Two Hezbollah members fighting alongside Syrian government forces in the Qusayr area near the border with Lebanon were killed on Monday, a source close to the Lebanese Shiite militant group said.
"Two members of Hezbollah who went to Syria to fight against armed groups in the Qusayr sector have been killed," the source said.
On February 16, three Shiite Lebanese trained by Hezbollah were killed in fighting in the same area, according to the Syrian Observatory for Human Rights.
A Hezbollah source said at the time that the three were residents of Syria and had died defending themselves.
But the two killed on Monday were residents of Lebanon, the source said, without revealing their identities.
The group has acknowledged that its members living in Syrian villages on the border with Lebanon have taken part in battles against "armed groups" in self-defence.
But it refuses to discuss allegations by Syrian rebels that it has sent fighters from Lebanon to bolster the forces of its ally, Syria's President Bashar al-Assad.