WASHINGTON — The United States has repatriated and charged the last Americans believed to be detained in Syria and accused of supporting the Islamic State, the Justice Department said on Wednesday. The move could give the Trump administration a stronger hand in its efforts to persuade other nations to repatriate and, when appropriate, prosecute citizens who traveled to the Middle East to support the group.

The Justice Department said that the four repatriated Americans were among about 2,000 men from dozens of countries who were imprisoned in northern Syria and caught for years in legal and political limbo. The four were captured and detained last spring by the Kurdish-led Syrian Democratic Forces.

“This is a significant moment in what has been a yearslong effort to bring back the individuals who left the U.S. to fight with ISIS,” John C. Demers, the head of the Justice Department’s National Security Division, said in an interview. “Each country should take responsibility for the people who left their countries.”

Two of the suspects, Emraan Ali and Jihad Ali, a father and son, made their initial appearance in federal court in Miami on Wednesday. Emraan Ali traveled to Syria in March 2015 with his family, including his son, and received military and religious training from the Islamic State, the government said in court documents. Mr. Ali and his son were accused of providing, trying to provide and conspiring to provide material support to the group. They were captured in 2019 during one of the Islamic State’s final battles to maintain its territory in Syria, the Justice Department said.

Two other suspects, Abdelhamid Al-Madioum and Lirim Sylejmani, were charged two weeks ago in federal courts in Minnesota and Washington, D.C., with supporting the militant group, efforts that began in 2015, according to court documents.

Though both the Obama and the Trump administrations decided to repatriate and try American detainees, other countries have been reluctant to bring back terrorism suspects because of political and legal hurdles.

But members of the Syrian Democratic Forces are unlikely to be able to detain the rest of the prisoners long-term, particularly as the civil war in Syria continues under President Bashar al-Assad. The Treasury Department on Wednesday also imposed sanctions on nearly 20 people and entities, including the governor of the Central Bank of Syria, in an attempt to restrict funding to Mr. Assad and his government.

Should those international prisoners be released with no plan to charge them or reintegrate them into society, they could pose a terrorist threat.

“We are demonstrating to our international partners that it is not a long-term solution to leave their people imprisoned in Syria,” said John Brown, the F.B.I.’s executive assistant director for national security.

Mr. Brown said that the United States had offered other nations, especially in Western Europe, evidence and intelligence to help them bring charges against the prisoners as well as assistance in drafting legislation to overcome legal hurdles to repatriate their citizens.

The charges against the four American suspects are also the latest example of the Justice Department using the civilian court system to prosecute terrorism cases as the military commissions system at the wartime prison in Guantánamo Bay, Cuba, has foundered.

The debate over the use of civilian courts that persisted during the Obama administration has receded as prosecutors repeatedly secured convictions on terrorism charges and judges imposed lengthy sentences on them.

“We’ve done hundreds of terrorism cases in U.S. civilian court since 9/11, and very successfully so,” Mr. Demers said. He said that prosecutors also protected classified information in bringing their cases, putting to rest fears among some in the intelligence community that trials would expose sensitive information and diminish the government’s ability to fight terrorism.

“The system has worked,” Mr. Demers said. “It is something we will continue to use in this administration.”

In all, the United States has repatriated 27 Americans from Syria and Iraq, 10 of whom were criminally charged. The other 17 are the family members of Islamic State suspects or minors who were not charged with crimes.

Mr. Demers said that other Islamic State suspects who have been charged who were not in detention facilities and may also be brought back to the United States to face trial.

Mr. Brown said that the Islamic State was still active and no longer had to entice recruits to travel for indoctrination and military training. Long before its self-declared caliphate in Syria and Iraq collapsed, the group had begun using social media to recruit members and inspire others to act on their own to conduct terrorist attacks.

Charlie Savage contributed reporting.