The Islamic State’s recent defeats on the battlefield signal that its once-vaunted militia army has been hobbled by worsening money problems, desertions and a dwindling pool of fighters, analysts and monitoring groups say.

U.S.-backed Kurdish and Arab forces have seized significant amounts of territory from the extremist group in the parts of Iraq and Syria where it declared a caliphate in 2014. Those losses are linked to the group’s struggles to pay fighters and recruit new ones to replace those who have deserted, defected to other militant groups or died on the battlefield, the analysts say.

“These issues suggest that as an entity that is determined to hold onto territory, the Islamic State is not sustainable,” said Jacob Shapiro, an expert on the Islamic State who teaches politics at Princeton University.

[Islamic State strikes back in Syria after losing ground]

Only a year ago, the Islamic State was seen as a juggernaut — rich, organized and fielding thousands of motivated fighters — that overran rival forces in Iraq and Syria with astonishing speed and brutality.

But in recent months, its momentum has been reversed.

U.S. military officials estimate that the group has lost as much as 40 percent of the territory it held in Iraq and as much as 20 percent in Syria. Kurdish and Arab forces, including Iraq’s increasingly competent military, have advanced against the group with the help of airstrikes from a U.S.-led coalition.

The air raids have damaged the Islamic State’s oil infrastructure, a key revenue source, and the territorial setbacks have stripped the group of populations to tax and assets to seize, analysts say. All of this, they say, appears to have forced the group to reduce salaries and benefits for fighters.

Few expect a sudden defeat of the conservative Sunni group, known for its resilience and ability to surprise its opponents. It also will probably continue exploiting sectarian grievances that have helped it gain loyalty, albeit sometimes tenuous, from the largely Sunni populations under its control, an issue that has made it difficult to defeat the group.

Moreover, the suspension on Wednesday of U.N.-backed peace talks in Geneva to end the Syrian war may complicate international efforts to fight the Islamic State, also known as ISIS and ISIL. The United States and Russia back opposing sides in the conflict but have nevertheless supported the talks because of concern that the fighting, which has killed more than 250,000 people and displaced millions, is empowering the Islamic State.

Yet there appears to be a rise in the number of Islamic State fighters who have deserted or, in the case of the Syrian conflict, defected to other militant groups, said Vera Mironova, an expert on armed groups in Syria and Iraq at Harvard University’s Belfer Center. The salary and benefit cuts have caused “for-profit militants” in Syria to increasingly “look for better deals” with other armed factions, she said.

The group, she added, also is struggling to replenish ranks of its foreign fighters, who tend to be more ideologically driven but also die in relatively large numbers on the battlefield. Tighter border restrictions imposed by Turkey have slowed the flow of fighters into neighboring Syria, said Mironova, whose research has involved hundreds of interviews with militants who are fighting in Syria and Iraq.

“They’re in big trouble,” Mironova said, referring to the Islamic State’s ability to fight.

[Iraqis think the U.S. is in cahoots with the Islamic State]

Members of the Raqqa is Being Slaughtered Silently group, which monitors the Islamic State, say a rising number of foreign members of the militant group have requested help to flee Syria. The requests have been made secretly because the Islamic State regularly executes foreigners who attempt to escape, said a co-founder of the Syrian monitoring group, Mohammed Saleh, who like other members uses a nom de guerre because of threats from the militants.

“There are lots of these people who are desperately trying to flee, and not just from Raqqa,” he said, referring to the city in eastern Syria that is the Islamic State’s self-declared capital.

“Part of this is that these people are moving from vibrant cities like London or Paris. After a year of living in a place like Raqqa, they get tired of living without electricity and getting bombed all the time. They get bored, or they realize that the so-called caliphate is not what they were told it was.”

Analysts speculate that the problems have compelled the group to adopt new tactics, such as carrying out attacks abroad. That includes the Paris assaults in November that killed 130 people.

Attacks abroad may be an attempt to sustain the group’s narrative as always on the offense — which has been key for attracting potential militants. Even so, the Islamic State’s media narrative has shifted from a triumphant one to having to explain why it is losing so much, said Nelly Lahoud, an expert on political Islam at the International Institute for Strategic Studies who studies the group’s media.

“They overplayed their card at the beginning by describing their victories as a sign from God, a reward for their faith,” she said.

In October, the Islamic State announced a month-long amnesty for deserters, according to documents obtained and translated by Aymenn al-Tamimi, an expert on the Islamic State. He called the amnesty the “clearest sign” of the Islamic State’s troubles waging war.

According to activists with Raqqa is Being Slaughtered Silently, the Islamic State is also forcibly recruiting more teenage boys in Syria to fight for the group.

Analysts and monitoring groups say they have observed more reports of the Islamic State executing fighters who deserted during recent battles against Kurdish peshmerga fighters in Iraq’s north and Iraqi forces in the city of Ramadi.

Reliance on such extreme measures “is a sure sign of low cohesion and a burned-out military force,” said Shapiro of Princeton.

Read more:

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Today's coverage from Post correspondents around the world