Syria's opposition is accusing the Lebanese Hezbollah movement of declaring war on the Syrian people amid reports the Shi'ite militia's fighters have joined government forces in a battle against rebels in the central province of Homs.
Anti-government activists in the Syrian town of al-Qusayr, outside Homs, have reported mounting Hezbollah casualties in the last week as fighting heats up in the strategic pocket along the Lebanese border.
The opposition Syrian Revolution General Commission said Free Syrian Army forces killed 18 Hezbollah fighters in clashes earlier this week.
An activist who uses the pseudonym Abo Emad said that Hezbollah has been firing rockets into the area from the hills above Lebanon's northern Bekaa Valley for months. He said FSA fighters retook two villages in the fighting, capturing 10 Hezbollah militiamen and killing a commander.
"We took some prisoners and have their [identification cards]," said Abo Emad. "Because of the clashes and the battle we now have 10 prisoners and a lot of [additional Hezbollah fighters] were killed," he said.
The extent of Hezbollah's engagement in Syria cannot be independently verified.
Long an ally of Syria's President Bashar al-Assad, Hezbollah has denied involvement in the Syrian fighting, saying it is helping Lebanese Shi'ites living in border towns and villages to defend themselves against rebel assaults.
But the group's recruitment efforts have increased the flow of Shi'ite fighters crossing the border, according to Matthew Levitt, director of the Washington Institute's Stein Program on Counterterrorism and Intelligence
"Some of the people who are going to fight are actually Hezbollah. Some of the people more recently who are going to fight are Hezbollah militias they have created - popular committees they call them," Levitt said.
He put at 200 the number of known Lebanese Shi'ites killed in Syria over the last two years - an estimate he said comes by a count of reported martyrs' funerals for those with a "clear connection to Hezbollah."
Most experts agree the Lebanese militia has been involved in the Syrian conflict almost from the start.
The U.S. Treasury Department last August announced an extension of sanctions against Hezbollah for its support of the Syrian government, accusing the group of providing training, advice and extensive logistical support to Assad's military campaign.
Paul Salem, director of the Carnegie Middle East Center
in Beirut, said the Assad government "some time ago effectively handed over defensive security responsibilities" to Hezbollah for a number of Shi'ite villages in the al-Nabak area north of Damascus.
But he said the militia's involvement in offensive operations in rebel-held territory has escalated mostly in the last 10 days.
"What's new is the fighting in a slightly different area, near Qusayr, further north, between the city of Homs and the region further west," Salem said. "That is not an area of Shi'ite villages, not an area where Hezbollah previously had a social and political presence," he added.
Liberating Sunni-held territory around Homs is crucial to preparing a possible retreat for Syrian government leaders to coastal provinces that are a stronghold Assad's minority Alawite sect, an offshoot of Shi'ite Islam.
"Hezbollah has a particular role in helping the Syrian regime maintain a strategic belt that links the capital to the northwest Alawi homeland," said Salem.
Among Hezbollah's numerous reasons to want a so-called "Alawistan" along Syria's western coast, Levitt said, the most important is to "maintain a land bridge for the resupply of Iranian weapons."
Traditionally, most of Hezbollah's arsenal is smuggled into Lebanon from Syria. But the fall of the Assad government would complicate Hezbollah's ability to restock following a future war with Israel.
Creating and maintaining an Alawite enclave would ensure continued access to the sea through the ports of Tartous, Banias and Latakia, allowing the weapons flow to continue via the secured corridor.
"The group is part of a broader Iranian alliance system [and] it doesn't want that system to break in Damascus. The Iranians are helping, Hezbollah is helping, Iraq's Maliki government is reluctantly helping," Salem said.
A major political and military force, Hezbollah was assisted by the Syrian regime when it occupied Lebanon during its civil war. Syria, too, has been a conduit for helping Hezbollah maintain its strong relationship with Iran.
Hezbollah is considered a terrorist group by the United States and Israel.
Fears for Lebanon
The Syrian opposition's new interim leader, George Sabra, said in Istanbul this week that "the Lebanese president and the Lebanese government should realize the danger" that Hezbollah poses to the lives of Syrians and regional relations.
Days later, two Lebanese Sunni sheikhs issued fatwas urging their followers to join Syrian rebels fighting to oust Assad, calling their struggle a "jihadist duty."
The Syrian government has attacked suspected rebel supply routes inside Lebanon with artillery and warplanes. But conditions in Syria are also pushing pro-Assad forces into the northern Bekaa Valley.
"If you want to move from Damascus into [Syria's] Alawi areas now, whether you are Hezbollah or the Syrians, the only assured way to go is through the Bekaa because the territory between the capital and traditional coastal Alawi enclaves is not controlled by the regime," Levitt said.