Although Hizbullah forces have been active in Syria for a long time, they had largely been confined to training and advisory roles, usually under the cover of protecting the Sayyida Zainab shrine in Damascus or Lebanese Shi'a villages which, by some quirk of cartography, were actually within Syrian territory.

Hizbullah's central role in offensive operations for the battle for Qusayr, however, resulted in many casualties and an acknowledgement that the group's presence could no longer be hidden. Hizbullah Secretary-General Hassan Nasrallah subsequently went public about the group's active support of the Assad regime. The success of Hizbullah's fighters in Qusayr helped the Syrian Government regain military momentum, and Assad's forces continue to press their advantage in Homs and Damascus.

During my visit to Lebanon in April I was advised that the creeping involvement of Hizbullah in Syria was the cause of some heated debate within the pro-Hizbullah Lebanese Shi'a population, but that the increasingly sectarian nature of the conflict and the presence of Salafi jihadists (with backing from Gulf Arab supporters) had effectively silenced the debate; support for Hizbullah's Syrian adventure is now solid within the community.

It now appears that Hizbullah's opponents have decided to take the fight to Hizbullah on its own territory.

Earlier this month, a car bomb targeted the Bir al-Abd area of Beirut's southern suburbs, the heartland of Hizbullah support. Two days ago, a Hizbullah convoy was struck by an IED inside Lebanon, allegedly on its way into Syria.

Normally, most Western states would be happy to see Hizbullah targeted militarily. But these are not normal times, and the fear of Sunni jihadists spreading their influence outside Syria is greater than that of Hizbullah, which at least has a disciplined command chain that can control its constituent elements. 

Terrorist activity by these jihadists in Lebanon is also likely to erode support for the Syrian opposition in Lebanon. One only needs to look at the attitude of Lebanese to the Palestinians, the jihadists in Nahr al-Barid in 2006 or Sheikh Assir's supporters in Sidon to understand how the Lebanese population judges the hierarchy of threats to Lebanon's sovereignty.

So serious have the threats been from al Qaida-aligned groups that there are even reports the CIA has provided warnings to Hizbullah, via Lebanese intelligence, about threats from these groups. If true, it means the US is providing support to the Syrian opposition at the same time as it provides threat warnings to Assad's supporters. Is it any wonder President Obama wants as little as possible to do with the Syrian morass?