The defection of Syria's prime minister was a boon for the opposition, heightening regime paranoia, but as rebels and their allies await mass defections, analysts say the ruling core remains intact.

The difference between a trickle of defections and a division or battalion changing sides could tip the scales in favour of the opposition, says Wayne White of the Washington-based Middle East Institute.

"You could literally turn around a unit like that, and it's a more potent weapon than rebel forces because it has more equipment, a chain of command and fights in an organised fashion with heavier weaponry."

But the absence of mass army defections shows there are "still a sufficient number of Sunni Arabs throwing their lot in with the regime."

"Of the officers above rank of colonel, I estimate that two thirds are not Alawites," White says.

The regime "needs 20-30 percent of them to remain loyal to stock the army with infantrymen and government with administrators to keep things going -- and that may be what they have."

While the Republican Guard and the elite Fourth Armoured Division are expected to remain loyal, it is puzzling to observers that regular divisions which "are even more heavily Sunni" have not broken ranks.

"A division is made up of many battalions. Why hasn't one battalion defected and just gone over to the other side?" asks White.

"The US and Turkey are waiting for this, hoping for this, wondering why it's taken so long."

But with the rebellion is now in its 17th month and the core leadership -- the family of President Bashar al-Assad and the top echelon of the military and security services -- remains intact.

This is despite billions of dollars reportedly pledged by Saudi Arabia, Qatar and Kuwait to encourage high-level defections, according to a Gulf-based diplomat.

According to a Lebanese security official, there are about 1,200 brigadier generals in the Syrian army, and only about 40 have defected. In contrast, there are only about 100 senior-ranking generals, all of who remain loyal.

As for the civilian leadership, even the defection of premier Riad Hijab, a Sunni, was not "the death blow," Lebanese former minister Marwan Hamade says.

Remaining high-ranking Sunni civilians "are limited to very few names, principally Foreign Minister Walid Muallem who has never been an influential part of the regime, and others who have vanished from the public scene," he says.

White says: "The PM is a figurehead in this country, deliberately placed because he was a Sunni, to try to appeal to Sunnis in the Damascus area."

In contrast, the security services are heavily Alawite: "This is a job you don't farm out to your collaborators."

Just two key Sunnis remain in security, according to Hamade, citing Ali Mamluk, newly appointed chief of intelligence, and Rustom Ghazali, former head of military intelligence in Lebanon "who is implicated in many murders."

"Their futures are bleak anyway," Hamade says. "The chance for them to remain in any future Syria is almost nil."

The importance of Hijab's defection, he says, is that it "concerns an old time Baath party member" who rose through the ranks.

"What sends a chill through regime is that people in every level of government can find the opposition... that people know if they want to do something like this, who they contact and where they go," White says.

"This produces ripple effect of arrests and interrogations to find out who is responsible, who let their guard down -- a witch-hunt."

"To the extent that witch-hunts occur, the regime is being eaten away from the inside."

Each defection sees the security apparatus wrap the noose more tightly around high profile leaders who remain.

Analyst Aram Nerguizian of the Washington-based Centre for Strategic and International Studies says: "Now there is a degree of internal paranoia and control that make it incredibly difficult for defections at the senior level.

"When there's one pilot who defects, it makes it more difficult for others. They may be grounded or vetted to make sure they don't pose a risk."

According to Andrew Tabler, analyst at the Washington Institute for Near East Policy, "the Sunni veneer that Hafez al-Assad created in the 70s is coming off... but "the core is still intact."

Nerguizian says that with the Alawite leadership finding their backs against the wall, they are "that much more dangerous in their decision making.

"The regime still does have strong nuclei of Sunni support, but that is whittling over time."

"Many outside and inside the regime look at the scale of the crisis, which is increasingly sectarian in nature, and find themselves in support of an increasingly minority-led regime.

"This is both a strength and a weakness: a strength because common interests tied to communal survival make the current struggle an existential one for both the regime and the Alawite community," says Nerguizian.

"A weakness because alienating a majority Sunni Syrian population is an untenable strategy for long-term stability."