A former Middle East adviser to Barack Obama has called on the U.S. President to reverse course in Syria and begin – finally – to bomb the regime of Syrian President Bashar al-Assad, rather than attacking Islamic State jihadi forces.

Dennis Ross, who served as Mr. Obama's senior adviser from 2009 to 2011, as well as in the administrations of presidents George H.W. Bush and Bill Clinton, said that bombing Syrian bases is "the language Mr. Assad and [his ally, Russian President Vladimir] Putin understand."

The very threat of such strikes should persuade Mr. Putin to "make Mr. Assad behave," Mr. Ross wrote in an op-ed article in Wednesday's New York Times

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"The threat of such strikes is probably the only way to start a political process to end the war," he concluded.

This aggressive proposition has come even as the White House prepares to co-operate with Russia in waging a joint campaign against IS fighters in the north and east of Syria. Both Washington and Moscow are pledging to share intelligence with the other and to co-ordinate air strikes.

The agreement with Russia is "riddled with dangerous loopholes," said Mr. Ross, who wrote that he has seen a leaked text of the proposed arrangement. It would allow Syrian and Russian forces to continue attacking moderate rebels, he said.

Not only that, he believes it would solidify the Assad regime's hold on power, maintain its siege of the opposition-held city of Aleppo and push terrorist groups and refugees into neighbouring Turkey.

The controversial recommendation also came just a day after the Pentagon confirmed that U.S. forces have opened up another front against Islamic State in Libya. There, both unmanned and manned U.S. fighter aircraft have begun firing missiles at IS positions in Sirte, an area in central Libya long held by fighters loyal to Islamic State.

In Syria, Iraq and Libya, the campaign against IS forces is viewed by Washington as more than just a visceral reaction to the jihadis' barbaric executions of Western prisoners. It is meant to end the threat of their terrorism in the West as well as to establish or to preserve moderate governments in each of these war-torn Arab states. And it is meant to achieve all this without putting many U.S. boots on the ground.

That would be the risk in attacking the Assad regime, Mr. Ross acknowledged. It could "prompt Russia to escalate the conflict and suck the United States deeper into Syria."

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But that doesn't necessarily have to happen, he insisted. "These strikes would be conducted only if the Assad government was found to be violating the very truce that Russia says it is committed to," referring to a truce agreed on earlier this year by the opposition and by Syria and its allies. The agreement to limit the use of certain weapons has routinely been violated.

"Notifying Russia that this will be the response could deter such violations of the truce and the proposed military agreement with Moscow," he wrote. "In any case, it would signal to Mr. Putin that his Syrian ally would pay a price if it did not maintain its side of the deal."

A leading Israeli analyst would go surprisingly further than Mr. Ross in redirecting U.S. actions: Under no circumstances should Islamic State be destroyed, said Efraim Inbar, director of the Begin-Sadat Centre for Strategic Studies. It would be "a strategic mistake" to do so.

Under the present circumstances, facing powerful armed forces, Islamic State can do little to capture more territory or inflict more harm. There is no need, he argued in a paper published Tuesday, to finish off the group.

Rather, "a weak Islamic State is, counterintuitively, preferable to a destroyed Islamic State," he insisted. If fully defeated, the group's fighters would soon flow home to Western and other states and cause a great deal of trouble.

On the other hand, "prolonging the life of IS probably assures the deaths of more Muslim extremists at the hands of other bad guys in the Middle East, and is likely to spare the West several terrorist attacks," he argued.

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Defeating IS forces would also help the Assad regime win the civil war in Syria, he argued. That in turn would strengthen the Russian grip on Syria and encourage Iran's hegemony in the region.

"The Western distaste for IS brutality and immorality should not obfuscate strategic clarity," Mr. Inbar said.

The U.S. administration, he ruefully concluded, "does not appear capable of recognizing the fact that IS can be a useful tool in undermining Tehran's ambitious plan for domination of the Middle East."