Hezbollah Secretary-General Hassan Nasrallah this week denied allegations that FSA forces killed his deputy, Naim Qassem. FSA has stepped up rhetoric saying Hezbollah, a Syrian government allay in Lebanon, is engaged in the Syrian civil war.
"For months Hezbollah has been shelling targets in the Syrian governorate of al-Qusair from Hermel in Lebanon," FSA spokesman Louai al-Meqdad told the BBC, referring to border regions.
He added that Hezbollah fighters are suspected of taking up positions in Syrian cities near the Lebanese border.
The influence of Damascus loomed large in Beirut before Lebanon's Cedar Revolution in 2005 forced Syrian military forces out of the country. A Lebanese judge called recently for the death penalty of a former Lebanese minister and a Syrian general accused of plotting attacks from Damascus.
Nasrallah said, during a televised address this week, that Hezbollah forces were only taking a defensive posture against Israel.
"We are very, very keen on preventing confrontation but no one should make any miscalculations with us," he said.