As fighting in the Syrian city of Aleppo intensified, with the death toll topping 250 in little more than a week, US Secretary of State John Kerry intensified his own efforts to reestablish the cease-fire that first took effect in February.

But, after meeting with the United Nation's special envoy to Syria, Staffan de Mistura, in Geneva, the usually upbeat Kerry struck a rather downbeat note, saying the conflict was "in many ways out of control and deeply disturbing to everybody in the world, I hope."

The original cease-fire agreement didn't even include the strategic town of Aleppo, although the situation had been relatively calm there until little more than a week ago. Since then, however, Bashar al-Assad's regime has been accused of deliberately targeting a major hospital and three clinics, which Kerry called, "unconscionable" and adding that "it has to stop."

But experts agree that making it stop will be difficult. The Assad regime, with the military backing of Russia and, to a lesser extent, Iran, may be perpetrating the violence, but analysts say US President Barack Obama made a strategic blunder by keeping the US out of the conflict.

"The US has no stake in it militarily or politically," said David Butter, a Middle East expert at the Royal Institute of International Affairs in London. "There is a residual sense that the US is the number one military and political power in the world, and if there's a crisis the US has to take some interest."

Kerry works to restore cease-fire

Yes, Kerry is working with the UN envoy and his Russian counterpart, but Butter and others say that, by keeping the US military out of Syria, the White House left itself without any leverage to influence events, including a peace process in the worn torn country, which has now claimed more than 270,000 lives since 2011.

Itamar Rabinovich, another Middle East expert with the Washington-based Brookings Institute, said Obama didn't need to inject US soldiers into Syria's civil war in order to give Washington some negotiating power.

"One can make a big difference with a no-fly zone," he said. "It could have established a safe haven in northern Syria along the Turkish border."

That, however, would have been a more viable option before Russia made a stark military commitment to the Syrian regime last summer, Rabinovich said, explaining that a US-led no-fly zone would difficult, if not impossible, to implement now.

A handful of US military advisers, no more than 50 or so, is all that Washington has inside Syria. That won't give the US the desired leverage it needs to bring the Syrian regime and its military patrons to heel, the experts say.

Currently, the Assad regime has no incentive to negotiate a cessation of hostilities because, for now at least, neither the potpourri of rebels inside Syria nor any outside military force poses an existential threat to the regime.

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If a cease-fire is achieved, Butter says it will be because the Russian's want to look like peacemakers - in effect using the US.

"Russia likes having the United States involved because it gives their (peace) effort legitimacy," he said. "Putin said military gains could be capitalized on by bringing in the US to legitimize the peace process."

He predicts that Syria is poised to enter a period of fragile cease-fires that will collapse and be patched together, only to see the cycle repeat itself for the foreseeable future - perhaps until a new president takes office in Washington.

No US leverage means more war

Without the necessary leverage to compel the warring sides to negotiate - and compromise - Rabinovich, from the Brookings Institute, says the process can't go forward.

That process, he said, should look like this:

A) a consolidated and durable cease-fire

B) agreement on a political solution

C) implementation of the agreement

He said the conflict in Syria reminds him of the long, drawn-out civil war that broke out in Lebanon in the 1970s and dragged on for 15 years.

"I'm pessimistic…with all due respect to Secretary Kerry," he said. "President Obama is determined not to be drawn into Syria, and Russia is determined to keep Assad in power."

Butter agrees that there is no end in sight to Syria's civil war, but he questions the Kremlins' affinity for the Syrian strongman.

"Russia doesn't have the leverage to pull strings inside the (Syrian) regime," he said. "Assad is a very difficult entity to deal with, very slippery, saying one thing and doing another. They're stuck with him."