UNITED NATIONS — Its fighters have seized oil fields, held water supplies hostage, and commandeered heavy artillery that the United States once supplied to a friendly government in Iraq. In late July, they decapitated Syrian soldiers, put their heads on fence posts and published photographs online. For the last five days, they have drawn the Lebanese Army into a firefight over control of a border town, their first territorial foray into Lebanon.
The group, the Islamic State in Iraq and Syria has attracted fighters from around the globe. It is on nearly every nation’s public enemy list, as well as the United Nations’ list of terrorist organizations facing sanctions.
International cooperation to check the organization’s rise has so far proved elusive, even as its influence has hurt the interests of world powers and complicated the regional rivalries among Iran, Saudi Arabia and Turkey. Among its latest victims are members of an Iraqi minority group, the Yazidis, who have been hiding in the mountains.
“You say you don’t like ISIS,” said Michael Stephens, the Qatar-based deputy director of the defense analysis group of the Royal United Services Institute, a research group headquartered in London. “What do you do about it?”
For the United States and Europe, Mr. Stephens and others said, supporting the Shiite-dominated Iraqi government wholeheartedly is tricky because that sends the wrong message to Sunni-led Persian Gulf allies. Backing the Kurds is tricky because neither Iraq nor Turkey wants its Kurdish territories to secede. Supporting the government of President Bashar al-Assad of Syria in fighting his ISIS opponents is impossible, given the efforts to unseat him for the last three years. “There are so many variables here,” Mr. Stephens said. “Any action will have so many unintended consequences.”
The United States has made some effort in recent weeks to counter ISIS and affiliated extremists. On Wednesday, the Treasury Department announced targeted sanctions against those believed to finance the group, including one known by six aliases, who it said had helped send money from Kuwait to fighters based in Syria.
In June, the White House announced $500 million in additional aid to moderate rebels in Syria, while warning of the dangers of weapons’ falling into the wrong hands. Late last year, it rushed weapons to Iraq — and in June, after the militants took over Iraq’s second-largest city, Mosul, President Obama announced he was sending up to 300 military advisers to aid the Iraqi Army.
There are nascent efforts in the United Nations Security Council, too, which reflect the difficulties of international consensus on ISIS. The Council last week issued a statement, drafted by Russia, reminding countries not to buy oil from the group, leaving unclear exactly who was buying the oil. The opposition Syrian Coalition maintains that the militant group sells oil to Mr. Assad’s government even while trying to topple it.
On Tuesday, the Council issued a second statement, drafted by the United States, calling on all Iraqi communities to unite against “this violent and senseless threat to Iraq’s unity, identity and future.” It did not say anything about supporting the government in Syria, which would have been a capitulation to Russia. The Kremlin maintains that the world should back Mr. Assad in battling terrorism.
In fact, analysts of the region say, until recently, the Assad government had not devoted much energy or firepower to battling ISIS, mainly because their interests converged. Mr. Assad and ISIS wanted equally to sideline other rebel groups, including moderate factions backed by the West.
Now, after having left each other alone, ISIS and Mr. Assad’s forces are increasingly clashing. In early July, Mr. Assad’s forces bombed the city of Raqqa, the group’s main base, according to witnesses there. The bombardment targeted what was believed to be an ISIS training camp, killing at least 20 fighters, the London-based Syrian Observatory for Human Rights reported.
In mid-July, the group seized a Syrian gas field, known as Sha’er, killing several Syrian soldiers. A week later came a suicide attack on a military base called Division 17, near Raqqa. Abou Osama, a university professor who lives nearby, said he saw the heads of soldiers displayed on the fence posts of the base.
These clashes partly reflect the difficulties any one country in the polarized region faces in confronting the group.
“With Iran and Saudi Arabia locked in a proxy war in Syria, Saudi Arabia competing with Qatar and Turkey for influence throughout the region, and Kurds — themselves hardly united — leaning ever further toward independence, it is not realistic to expect a coherent strategy for confronting ISIS to emerge from the region,” said Noah Bonsey, the Syria expert at the International Crisis Group. “The U.S. has the clout and capacity to build partnerships capable of reversing ISIS gains, but seems to lack the necessary vision and will.”
ISIS threatens not just Iraq and Syria. It has drawn fighters from countries as far-flung as India and China, Belgium and Britain. United Nations experts said fighters from rival jihadist groups, including the Nusra Front, an affiliate of Al Qaeda, have steadily defected to ISIS, because it has more money and guns. Military analysts say that it is exceedingly difficult to neutralize a group that now finances itself — it controls several oil fields in Iraq and Syria — and is heavily armed with weapons seized from both Iraqi and Syrian military bases.
American officials have said that Iraq lacks a military able to retake the territory it has lost to ISIS. Lacking sufficient ground forces, the government of Prime Minister Nuri Kamal al-Maliki has relied on air attacks that have killed civilians and become a rallying cry for militants to recruit new fighters. Human Rights Watch said in a recent report that at least 75 Iraqi civilians had been killed and hundreds wounded since early June in airstrikes on territory controlled by the group around the city of Falluja.
The United States has plenty of reason to worry, said Julia McQuaid, an analyst at the CNA Corporation in Arlington, Va., and not just because Western recruits to ISIS can come home and wreak havoc.
ISIS propounds the idea of a Sunni “caliphate,” which by definition threatens the borders of nation-states. “While there should be little concern for any current jihadist movement successfully establishing a global caliphate under its banner,” Ms. McQuaid wrote in a web article, the Islamic State’s model “may have profound implications on the security environment in other countries.”