A long-feared full-blown sectarian war in Syria and Lebanon is inching closer to becoming a reality, with Syrian opposition forces threatening to make a border area “a graveyard” for Hezbollah. The Shiite group and the largely Sunni Free Syrian Army (FSA) exchanged rhetorical and actual blows this week, in the aftermath of a pointedly-declined ultimatum issued by the FSA demanding that Hezbollah remove its forces from Syria. Hezbollah has been heavily involved in Iranian efforts to prop up the regime of Syrian ruler Bashar al-Assad, which the FSA and other opposition groups are seeking to overthrow.

Syrian opposition forces this week claimed several successful attacks against Hezbollah forces. An FSA spokesman today threatened the Iran-backed terror group with further attacks if the group deepens its involvement in the Syrian conflict:

“For months Hezbollah has been shelling targets in the Syrian governorate of al-Qusair from Hermel in Lebanon,” says Louai al-Meqdad, a spokesman for the Free Syrian Army… The Syrian opposition has accused Hezbollah of using [Lebanese] towns as a base to send fighters into Syria… According to Mr Meqdad, the Syrian regime seems to have handed over operations in al-Qusair to Hezbollah so its own troops can be redeployed to Damascus where they are more urgently needed. “Al-Qusair will be the graveyard of Hezbollah if they ever think of invading it,” he adds.

For his part Hezbollah chief Hassan Nasrallah accused the FSA of targeting Shiites in Lebanon, heightening analyst concerns that Hezbollah will use the accusation as a pretext for further action in Syria. He also issued his own threats:

Hezbollah leader Sayyed Hasan Nasrallah Wednesday issued a strongly worded warning against what he said were attempts to incite Sunni-Shiite strife in Lebanon, advising his rivals: “Don’t make any miscalculations with us.” He also said that Shiite Lebanese living in Syria had the right to defend themselves against rebel attacks, asking them to spare the lives of civilians.

Hezbollah officials have been working with their Iranian patrons to create a network of militias that could be activated in the event of Assad’s fall. A high-ranking Iranian Revolutionary Guard official was recently killed traveling between Lebanon and Syria. The FSA has claimed that in addition to striking convoys carrying Syrian and Hezbollah officers, it attacked and injured a top Nasrallah deputy. FSA officials continue to insist that they have evidence of Hezbollah taking up positions inside Syria.

The reports are in tension with some Western journalism, including articles published today, the effect that “little evidence has emerged of any military involvement on Hezbollah’s part.”

A video published earlier this week by the STRATFOR intelligence firm details the unfolding sectarian conflict: