ISTANBUL — When U.S. forces found Abu Bakr al-Baghdadi, the leader of the Islamic State militant group, he was not in some forgotten border town or remote patch of desert but in Syria’s Idlib province, a place where Baghdadi surely knew he was surrounded by enemies, and eyes.

The province, a major battlefield in Syria’s civil war, is dominated by an Islamist militant movement hostile to the Islamic State. In the skies, Syrian and Russian warplanes are ever-present, carrying out bombing raids to help the government of President Bashar al-Assad recapture Idlib, Syria’s last rebel-held bastion.

 Observation posts manned by Turkish soldiers dot the province. Three million people live or shelter there, in a place only slightly larger than Delaware and nearly impossible to escape.

It is unclear how long Baghdadi had been in Idlib or what he was doing there. But the province where he died — with its refugee camps, its front lines, its unshakable sense of dread — stands as a stark reminder of the misery and threats still radiating from Syria’s civil war.

Western intelligence agencies are nervously monitoring the fighting in Idlib, which has become a proving ground for a new generation of extremists, in a war that has already bred thousands of hardened militants.

Since late April, the Syrian government’s offensive to retake the rebel-held territory has killed or injured more than a thousand civilians, according to the United Nations and human rights groups. More than 500,000 have fled the fighting in southern Idlib and neighboring Hama province. Syrian and Russian warplanes have bombed hospitals and schools.

Residents are left facing terrifying possibilities: the government’s military advance or the growing dominance of extremist rebels. People “do not have the option of picking who will take over or who won’t — they just want to stay alive,” said a political activist in Idlib. “It’s all bombardment and strikes and killing and death.”

Abu Bakr al-Baghdadi, the elusive Islamic State commander, died during a U.S. military operation in Syria. (Luis Velarde/The Washington Post)

Idlib is largely controlled by Hayat Tahrir al-Sham (HTS), a militant group that began as Syria’s al-Qaeda affiliate but reinvented itself several times during the civil war. HTS declared it was no longer affiliated with al-Qaeda in 2018. More-extreme Islamist militants left the group to form a smaller, hard-line faction, Hurras al-Din, which is the new al-Qaeda affiliate.

The Islamic State has a low-key presence in Idlib as well, with its fighters forming “sleeper cells” in the province, according to Dareen Khalifa, a Syria analyst with the International Crisis Group, who visited Idlib a few months ago. 

There was no obvious reason Baghdadi would have felt safe in Idlib, she added. The Islamic State had been targeted in raids carried out by HTS and was seen as an adversary by other militant groups, including Hurras al-Din.

How Baghdadi got to Idlib was not immediately clear. The province is surrounded by areas held by the Syrian or Turkish governments. A Turkish official said it appeared that Baghdadi had been in the area for at least 48 hours. A U.S. official said he had been there for “a while.”

In the area where he was found, control was divided between HTS, al-Qaeda-affiliated groups and Turkish-supported opposition, a senior State Department official said.

 Some feared that Baghdadi’s killing might actually make life harder for people in Idlib, by focusing attention on the border area near Turkey where he was cornered and killed, in a village called Barisha.

Baghdadi’s death “creates another type of horror for people,” said the activist in Idlib, referring to the possibility that the U.S. operation could lead to follow-up raids or factional fighting in an area just a few miles from one of Idlib’s largest camps for displaced people.

 “If Baghdadi was in the area, then the whole area is in danger,” said the activist, who spoke on the condition of anonymity because of fears of retaliation from the militant groups.

The violence and insecurity in Idlib show the challenges that remain even as a group of regional powers, including Syria, Iran, Russia and Turkey, are nominally cooperating in an effort to end Syria’s conflict.

Assad’s government forces are seeking to recapture the province as part of an effort to reestablish authority across the fractured country. Turkey, which is allied with Syrian rebel groups, has tried to prevent the Syrian offensive, fearing that it would send millions of refugees — as well as militants — surging across its border.

U.S. officials are alarmed at the growing sway of extremist groups but have also strongly opposed any Syrian government offensive against those groups — fearing that it would cause a new refu­gee exodus and that Assad’s government would use chemical weapons as part of its offensive, the State Department official said.

“Where we have conducted . . . anti-terrorist operations in Idlib, [it’s] because we’ve had very important targets,” a senior State Department official said. But even if the province contained tens of thousands of “terrorists,” he added, “that’s no reason to attack 3 million refugees and drive them into Turkey and Europe.”

President Trump, who has tried to reduce the U.S. role in Syria’s conflict, including by withdrawing some troops from the country, has tweeted about Idlib on several occasions. “Hearing word that Russia, Syria and, to a lesser extent, Iran, are bombing the hell out of Idlib Province in Syria,” he wrote in June. “What is the purpose, what will it get you? STOP!”

Since the government offensive intensified last spring, a shaky cease-fire has reduced the violence somewhat without solving the puzzle of Idlib’s future. The key player is Russia, which is trying to balance the demands of its Syrian and Turkish allies.

Although Russia had provided military backing for Syria’s offensive, Moscow might eventually be able to live with a portion of the province controlled by HTS, as long as such an area was “contained and protected by Turkey,” said Khalifa of the International Crisis Group.

But Syria had been unwavering in its demand that Idlib be returned to its control. Turkey had been just as determined to prevent an all-out offensive.

“Idlib is a huge interest for Turkey. There are 3 million residents, and thousands of jihadis they don’t want coming their way,” Khalifa said.

Asser Khattab in Beirut, and Karen DeYoung and Ellen Nakashima in Washington, contributed to this report.