– In the Syrian city of Raqqah on the banks of the Euphrates River, Islamic militants are busy building a capital fit for their followers.

Human rights observers say they have stoned women to death for adultery, while residents report that religious textbooks have been imported for schools and the market flooded with black cloaks for girls as young as 6. Even as it wages war on multiple fronts, the group has had time to focus on the details, recruit thousands into its forces and celebrate victories by parading the heads of its enemies.

It’s a reflection of how entrenched the group has become in Syria and how difficult it will be to uproot it from the country where it was able to assemble and train enough forces to push into Iraq in June. U.S. airstrikes alone won’t do it and the international community doesn’t have any other options to fall back on, Kamran Bokhari, vice president for the Middle East at Texas-based consulting firm Stratfor, said from Toronto.

“Who’s the other force that’s going to fight the Islamic State on the ground?” said Bokhari. “Its presence in Iraq is based on its strategic depth in Syria and to truly eliminate the threat from Iraq you have to weaken it in Syria.”

President Obama ordered airstrikes this month against the ISIL (the Islamic State of Iraq and al-Sham) terrorists in Iraq, and on Thursday he said he has asked military planners to come up with options that focus on Iraqi targets, but also include the possibility of strikes in Syria.

Syrian President Bashar Assad’s government, which has said that its three-year civil war has been against foreign- backed terrorists rather than freedom-seeking protesters, offered to cooperate in the fight against ISIL. On Monday, Syrian Foreign Minister Walid al-Muallem said any counterterrorism effort must be done in coordination with the Syrian government, a demand that the White House has ­dismissed.

French President Francois Hollande said Assad can’t be an ally in the battle against terror. Assad is an “objective ally” of the Islamic militants, Hollande told French ambassadors in Paris.

The United States is aiming to tackle ISIL without helping the Assad regime, though that may prove difficult, according to Michael Desch, professor of political science at the University of Notre Dame.

“This is a circle that can’t be squared,” Desch said by e-mail. “In both Saddam Hussein’s Iraq and now Assad’s Syria, we tried to overthrow brutal dictators only to find that their replacements were even worse.” ISIL “is far more of a threat than Assad and if attacking the former bolsters the latter, so be it,” he said.

ISIL, which evolved from Al-Qaida in Iraq, appeared in Syria two years after the anti-Assad uprising began, emerging in April 2013 following its break from the Al-Qaida-affiliated al-Nusra Front.

ISIL made its first statement from Raqqah in May 2013 with the public execution of three civilians wrongly accused of being army officers. They were Alawites, the branch of Shiite Islam that Assad belongs to. Mohammad, a Raqqah resident who declined to give his full name, said people are unhappy with the strict social codes.

Women cannot leave home without a male guardian, shops have to close five times for prayer and people accused of theft have their hands cut off in public, he said. “People yearn for the prewar days,” he said after arriving in Beirut. “But they’re too intimidated to speak out.”

ISIL on Wednesday killed dozens of Syrian soldiers it captured after seizing the Tabaqa military airport in Raqqah Province last weekend, Rami Abdurrahman, head of the British-based Syrian Observatory for Human Rights, said by phone. A video posted online by the Unified Media Center of Raqqah showed more than 100 men forced to march in their underwear at gunpoint.

Assad’s forces have engaged less with the group than other rebels partly because its brand of Islamic extremism fit the Syrian government’s narrative that terrorists are behind the insurgency and not activists seeking democracy.