"Beyond the tactical victories on the ground, the current strategy is failing," said Katherine Zimmerman, who wrote a recent report for the American Enterprise Institute entitled "Terrorism, Tactics and Transformation: The West vs the Salafi-Jihadi Movement."

"Every soldier and intelligence analyst that has worked on this problem understands what is happening," Zimmerman told AFP.

"They understand that what they are doing is a temporary solution. It's ending the immediate threat but not stabilizing or moving us forward. The problem comes down to policy and politics," she noted.

"It's easy to say, 'We're going to kill the person responsible for making the bomb.' It is much more difficult to say that our partner government has disenfranchised this group and it's one of the reasons why this person joins the terrorist group. And now he is the bomb maker."

Driven from lands it once held sway over in Syria and Iraq, the Islamic State group has returned to its origins as an underground jihadist outfit because the conditions that spawned it -- a deep discontent among most Iraqis and Syrians -- have persisted, experts say.

"The West is on the road to winning all the battles and losing the war," warned Zimmerman.

- 'Development problems' -

In a report last month on the resurgence of IS as a clandestine guerrilla group, the Center for Strategic and International Studies (CSIS) said that "while the United States and allied governments have weakened some groups like the Islamic State, many of the underlying causes have not been adequately addressed."

Those root causes include a "fragile state with weak or ineffective governing institutions" in areas affected by jihadist activity, where the Islamists can establish a sanctuary, the CSIS experts said.

They took maps showing areas where Al-Qaeda and IS were active and compared them to maps displaying "government effectiveness," based on World Bank statistics.

The result was clear: most of the countries where the insurgents are active -- Yemen, Syria, Iraq, Afghanistan, Libya, Mali, Nigeria, Somalia -- are also in the bottom 10 percent for government effectiveness.

At a conference this week in Washington, retired Marine general John Allen -- who once commanded US forces in Afghanistan and now heads the prestigious Brookings Institution -- said the West had to get ahead of the issue and ask, "Where should we be looking for the next problems?"

"We should spend a great deal more time looking at those areas that are in fragile or failing states," said Allen, who also served as presidential envoy to the international coalition battling IS.

"We have to recognize the hotspots where the human condition prompts the radicalization of large sectors of the population," he added.

"Often we join the conversation when the process of radicalization has been in place for quite a long time."

Allen noted that the problem is "a development issue, much more than a counter-terrorism issue."

At the annual conference on terrorism, organized by the Jamestown Foundation, many experts noted that in Iraq, the grievances of the Sunnis -- the branch of Islam that gave rise to Al-Qaeda and IS -- were compounded by the involvement of powerful Shiite militias both in the Baghdad government and in areas recovered from Islamist insurgents.

If those grievances were not taken into account, they warned, the jihadist groups were sure to be back.