The Biden administration is redoubling efforts to persuade countries to repatriate Islamic State fighters and their families from eastern Syria, but there are few signs the United States can quickly break an impasse that military leaders say is a major security threat.

Around 11,000 suspected fighters remain imprisoned in makeshift prisons run by Syrian Kurdish forces in northeast Syria. At least 60,000 women and children are confined to camps housing Islamic State families, where officials warn dire conditions and rampant extremism may yield a new generation of militants.

At least 70 people have been killed so far this year inside al-Hol, the sprawling camp that has come to symbolize the deadlock over the fighters and family members, hailing from across Europe, the Middle East and beyond, who now personify the unaddressed aftermath of the five-year battle against the Islamic State.

Many countries, including close U.S. allies in Europe, have been reluctant to bring home their nationals, citing security fears and the burden of monitoring or prosecuting those with extremist links.

“Just because it’s out of sight and out of mind, which it is for the vast majority of Americans, doesn’t mean it’s not a very serious problem,” said Nathan Sales, who oversaw efforts to repatriate those in the facilities as a top counterterrorism official during the Trump administration.

A senior State Department official, who spoke on the condition of anonymity to describe internal planning, said officials are working to help partner nations rehabilitate and prosecute repatriated militant fighters and relatives.

Officials say some countries, particularly in Central Asia and the Balkans, have welcomed back hundreds or thousands of their own nationals from Syria, primarily women and children. They declined to provide precise figures.

American officials are escalating their diplomacy on the issue as leaders of the Syrian Democratic Forces (SDF), the Kurdish-led group that has partnered with the U.S. military to battle the Islamic State, pleads for support to run detention facilities and find an alternative for those held inside.

At al-Hol — a massive outpost of flimsy tents housing 62,000 Islamic State family members, mostly women and children — conditions are deteriorating. Lodgings are ill-suited for extreme heat and cold. Sexual violence against women and children is common.

Camp officials and aid workers blame a spate of violent attacks on extremists in the camp and economic desperation. In recent months, militant facilitators and financiers have been found hiding inside camp facilities, suggesting the group is seeking to exploit lawlessness there to regain strength, officials said

Only a limited group of countries have brought home their citizens in significant numbers. Last week, local authorities in Syria said that Denmark and Germany had repatriated several dozen of their nationals.

Separately, some 11,000 men and boys suspected of militant activity remain detained in a network of poorly defended prisons. There have been several riots, and officials warn of possible prison breaks. Although the U.S.-led coalition has helped upgrade detention facilities, Kurdish officials say they are inadequate.

“We have urgent projects that we need to complete in other prisons,” SDF leader Gen. Mazloum Kobane said in an interview in August. “These people are living in schools and other buildings. The facilities are temporary. They’re not safe.”

American officials including Marine Gen. Kenneth F. McKenzie Jr., the chief of U.S. Central Command, has described the tens of thousands of children at al-Hol and other facilities as a time bomb.

“Unless we find a way to repatriate them, reintegrate them and de-radicalize them, we’re giving ourselves a gift of fighters five to seven years down the road, and that is a profound problem,” McKenzie said earlier this year.

The challenges around Islamic State detainees represent just one of numerous complexities of Syria’s civil war. While the Syrian government has not tried to push into SDF-controlled areas where the Islamic State prisons and camps are located, that could change, potentially putting them under state control, said Charles Lister, a Syria expert at the Middle East Institute.

“From a security perspective that is really terrifying,” he said.

American officials say the United States tried to set an example by repatriating 26 U.S. citizens from Syria and Iraq, including 12 adults. Another ­major element of the Biden ­administration’s strategy is a push to highlight the stakes of allowing the facilities to languish.

“We have to continue to make the case that it is a much more dangerous situation for these individuals to stay in northeast Syria than it is to be sent back home,” the State Department official said.

Complicating the diplomacy is the fact that close allies including Britain have declined to take back fighters in large numbers. The U.K. government has also stripped some of them of their citizenship.

A spokesman for the British embassy in Washington, who spoke on the condition of anonymity under ground rules set by the embassy, said the U.K. had brought unaccompanied or orphaned British children back from Syria.

“Our priority is to ensure the safety and security of the U.K.,” the spokesman said. “Those who remain in Syria include dangerous individuals who chose to stay to fight or otherwise support a group that committed atrocious crimes including butchering and beheading innocent civilians.”

Also key, U.S. officials say, is addressing the large population of Iraqis who make up at least half of those in the prison and camps.

According to Iraqi Foreign Minister Fuad Hussein, Iraq had repatriated its nationals when security screening was completed. U.S. officials say Iraq has taken some 1,700 people from Islamic State prisons and more than 400 family members.

But Iraqi security agencies have blocked the transfer of other families due to security concerns.

Welcoming back individuals with militant links is politically fraught for Iraq, especially after its punishing battle against the Islamic State. Officials bristle at foreign criticism when militants face prosecution in Iraqi courts. They say Western nations want fighters to be sent to Iraq but then point out flaws in its judicial system or condemn its use of the death penalty.

“The solution cannot be Iraqi only,” Hussein said in a recent interview. “It is an international solution.”

Experts say significant repatriation is unlikely in the absence of a dramatic change in Syria, such as a withdrawal of U.S. troops now arrayed alongside the SDF or a Turkish invasion deep into the country.

“I don’t see them going anywhere unless we see a serious trigger event,” Lister said. “Now, it’s just kicking the can down the road.”

Loveluck reported from London.