Damascus this week announced that government troops allied with Lebanon's Shi'ite Hizballah militia had recaptured the strategic Syrian border town of Qusayr after nearly three weeks of fighting.
But if Hizballah can now claim a first battlefield success in Syria, many analysts warn the victory only increases the risk the Syrian conflict will one day spark major sectarian conflicts in bordering countries.
Among the most worrisome dangers is that the conflict could blow back into Lebanon itself.
Fabrice Balanche, director of the French research center Gremmo in Lyon, says that is because much of the fighting in Qusayr was between opposing Lebanese Shi'ite and Sunni militants.
"The intervention of Hizballah in Syria is very significant because in Qusayr you also have Lebanese fighters, Sunni fighters, who are with the Syrian rebels," Balanche says. "So we can say that in Qusayr it is also a Lebanese war. It is not on Lebanese territory, it is just on the border, but you have Lebanese who are fighting each other."
He adds that the Syrian government's claim that Qusayr, 10 kilometers from the Lebanese border, is now secure does not mean the duel between Sunni and Shi'ite Lebanese fighters is over. Instead, it is likely to move to other fronts as Lebanese groups continue to funnel men, money, and weapons into Syria.
Hilal Khashan, professor of political science at the American University in Beirut, agrees. He says Salafist groups that are gaining a following in northern Lebanon are fighting a proxy war with Hizballah in Syria as they battle for influence within Lebanon itself.
"There are thousands of Lebanese Sunnis who are fighting in Syria as well, especially from northern Lebanon," Khashan says. "In his latest speech, Hizballah chief Hassan Nasrallah said, 'Let's not fight in Lebanon, anyone who wants to fight, let's go and fight in Syria.'"
No Sign Of Easing
Khashan says that, so far, there is no indication that either side wants to import their battle home to Lebanon, despite periodic clashes in Tripoli between supporters and opponents of the Syrian regime. He lists among the factors that discourage importing the conflict the Lebanese population's war-weariness after that country's own 1975-90 civil war and an apparent lack of interest among foreign countries in backing any factions seeking to restart the conflict.
Still, the confrontation between Sunni and Shi'ite Lebanese groups in Syria may provide the clearest example yet of how foreign fighters from regional countries are entering the Syrian conflict, choosing sides along sectarian lines, and engaging in a fight they could one day take back home with them.
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Among those fighters are militants from Iraq who are reportedly recruited by Iraq's own opposing Sunni and Shi'ite militias. The volunteers, often motivated by reports that shrines honored by their sect are being desecrated by enemies, gain combat experience in a conflict they see as much in terms of a Sunni-Shi'ite showdown as a Syrian civil war.
"I think at the simplistic level we have to look at this as a Sunni-Shi'ite divide, and there have been major wars between the Sunnis and the Shi'a in the past," Theodore Karasik of the Dubai-based Institute for Near East & Gulf Military Analysis warns. "When you look at the history of these wars, these wars do not last for a year, they are decades long. I think we have reached that Rubicon where we might see that Sunni-Shi'ite divide at war with each other in Syria and having it spread to places like Lebanon."
Despite the danger, none of the groups sending foreign fighters into Syria shows any sign of curbing their activities.
Hizballah has justified its intervention in the conflict as necessary to defend Lebanon against extremist Sunni groups like the Al-Qaeda-related Al-Nusra Front, which is also fighting in Syria.
Announcing Hizballah's deepening involvement in Syria in late April, the movement's head, Nasrallah, said the allies of Damascus would do everything necessary to save it. That suggested Hizballah was ready to fight anywhere in Syria as needed.
Analyst Khashan says Hizballah, which is backed by Iran, is highly motivated because its own survival depends upon the outcome of the war.
"Syria provides Hizballah's lifeline," Khashan says. "Hizballah's munitions, the travel of its personnel [to Iran], all take place through Syria. The loss of Syria would cause the disintegration of the Syrian-Hizballah-Iranian alliance. Therefore, Hizballah feels that by fighting in Syria they defend their very existence in Lebanon."
Extremist Sunni leaders equally seem to feel they are engaged in an existential conflict.
Following Hizballah's entry into Syria earlier this year, a leading Egyptian Sunni cleric based in Qatar warned that "Iranian Shi'a" were trying to "eat" Sunni Muslims.
The cleric, Yusef al-Qaradawi, on June 1 called on all who were able to undertake jihad to go to Syria to defend those being killed by the Syrian regime.