ANKARA, Turkey — Having spent most of his youth as a drug addict in one of the poorest neighborhoods of Turkey’s capital, Can did not think he had much to lose when he was smuggled into Syria with 10 of his childhood friends to join the world’s most extreme jihadist group.

After 15 days at a training camp in the Syrian city of Raqqa, the de facto headquarters of the group, the Islamic State in Iraq and Syria, the 27-year-old Can was assigned to a fighting unit. He said he shot two men and participated in a public execution. It was only after he buried a man alive that he was told he had become a full ISIS fighter.

“When you fight over there, it’s like being in a trance,” said Can, who asked to be referred to only by his middle name for fear of reprisal. “Everyone shouts, ‘God is the greatest,’ which gives you divine strength to kill the enemy without being fazed by blood or splattered guts,” he said.

As many as 1,000 Turks have joined ISIS, according to Turkish news media reports and government officials here. Recruits cite the group’s ideological appeal to disaffected youths as well as the money it pays fighters from its flush coffers. The C.I.A. estimated last week that the group had from 20,000 to 31,500 fighters in Iraq and Syria.

The United States has put heavy pressure on Turkey’s president, Recep Tayyip Erdogan, to better police Turkey’s 560-mile-long border with Syria. Washington wants Turkey to stanch the flow of foreign fighters and to stop ISIS from exporting the oil it produces on territory it holds in Syria and Iraq.

So far, Mr. Erdogan has resisted pleas to take aggressive steps against the group, citing the fate of 49 Turkish hostages ISIS has held since militants took over Iraq’s second-largest city, Mosul, in June. Turkey declined to sign a communiqué last Thursday that committed a number of regional states to take “appropriate” new measures to counter ISIS, frustrating American officials.

For years, Turkey has striven to set an example of Islamic democracy in the Middle East through its “zero problems with neighbors” prescription, the guiding principle of Ahmet Davutoglu, who recently became Turkey’s prime minister after serving for years as foreign minister. But miscalculations have left the country isolated and vulnerable in a region now plagued by war.

Turkey has been criticized at home and abroad for an open border policy in the early days of the Syrian uprising. Critics say that policy was crucial to the rise of ISIS. Turkey had bet that rebel forces would quickly topple the Syrian president, Bashar al-Assad, but as the war evolved, the extremists have benefited from the chaos.

Turkish fighters recruited by ISIS say they identify more with the extreme form of Islamic governance practiced by ISIS than with the rule of the Turkish governing party, which has its roots in a more moderate form of Islam.

Hacibayram, a ramshackle neighborhood in the heart of Ankara’s tourist district, has morphed into an ISIS recruitment hub over the past year. Locals say up to 100 residents have gone to fight for the group in Syria.

“It began when a stranger with a long, coarse beard started showing up in the neighborhood,” recalled Arif Akbas, the neighborhood’s elected headman of 30 years, who oversees local affairs. “The next thing we knew, all the drug addicts started going to the mosque.”

One of the first men to join ISIS from the neighborhood was Ozguzhan Gozlemcioglu, known to his ISIS counterparts as Muhammad Salef. In three years, he has risen to the status of a regional commander in Raqqa, and locals say he frequently travels in and out of Ankara, each time making sure to take back new recruits with him.

Mehmet Arabaci, a Hacibayram resident who assists with distributing government aid to the poor, said younger members of the local community found online pictures of Mr. Gozlemcioglu with weapons on the field and immediately took interest. Children have started to spend more time online since the municipality knocked down the only school in the area last year as part of an aggressive urban renewal project.

“There are now seven mosques in the vicinity, but not one school,” Mr. Arabaci said. “The lives of children here are so vacant that they find any excuse to be sucked into action.”

Playing in the rubble of a demolished building on a recent hot day here, two young boys staged a fight with toy guns.

When a young Syrian girl walked past them, they pounced on her, knocking her to the floor and pushing their toy rifles against her head. “I’m going to kill you, whore,” one of the boys shouted before launching into sound effects that imitated a machine gun.

The other boy quickly lost interest and walked away. “Toys are so boring,” he said. “I have real guns upstairs.”

The boy’s father, who owns a nearby market, said he fully supported ISIS’s vision for Islamic governance and hoped to send the boy and his other sons to Raqqa when they are older.

“The diluted form of Islam practiced in Turkey is an insult to the religion,” he said giving only his initials, T.C., to protect his identity. “In the Islamic State you lead a life of discipline as dictated by God, and then you are rewarded. Children there have parks and swimming pools. Here, my children play in the dirt.”

But when Can returned from Raqqa after three months with two of the original 10 friends he had left with, he was full of regret.

“ISIS is brutal,” he said. “They interpret the Quran for their own gains. God never ordered Muslims to kill Muslims.”

Still, he said many were drawn to the group for financial reasons, as it appealed to disadvantaged youth in less prosperous parts of Turkey. “When you fight, they offer $150 a day. Then everything else is free,” he said. “Even the shopkeepers give you free products out of fear.”

ISIS recruitment in Hacibayram caught the news media’s attention in June when a local 14-year-old recruit came back to the neighborhood after he was wounded in a shelling attack in Raqqa. The boy’s father, Yusuf, said that the government had made no formal inquiry into the episode and that members of the local community had started to condemn what they saw as inaction by the authorities.

“There are clearly recruitment centers being set up in Ankara and elsewhere in Turkey, but the government doesn’t seem to care,” said Aaron Stein, a fellow at the Royal United Services Institute, a London-based think tank. “It seems their hatred for Bashar al-Assad and their overly nuanced view of what radical Islam is has led to a very short- and narrow-sighted policy that has serious implications.”

The Interior Ministry and National Police Department did not respond to requests for comment.

On a recent afternoon in Ankara, Mr. Erdogan and Mr. Davutoglu came to pray at the historic Haci Bayram Veli Mosque, just over 100 yards away from an underground mosque used by a radical Salafi sect known to oversee ISIS recruits.

When news of their visit reached the neighborhood, several residents scurried down the steep hill hoping to catch an opportunity to raise the issue.

At the same time, a 10-year-old boy lingered in his family’s shop, laughing at the crowd rushing to get a glimpse of the two leaders. He had just listened to a long lecture from his father celebrating ISIS’ recent beheading of James Foley, an American journalist. “He was an agent and deserved to die,” the man told his son, half-smirking through his thick beard.