(CNN) A federal grand jury in Dallas on Thursday indicted an American ISIS suspect who had been transported back to American soil from Syria.

Omer Kuzu, who is 23, was charged with traveling to Syria and conspiring to provide material support to ISIS.

Kuzu, who was born in Dallas, traveled with his brother in 2014 from Houston to Istanbul and then was smuggled by ISIS into Syria, prosecutors say he told FBI investigators, according to court documents.

He eventually received weapons and other training in Mosul, Iraq, and then returned to Syria, where ISIS maintained the headquarters for its self-declared caliphate, according to the documents.

Prosecutors allege Kuzu was issued weapons and was paid the equivalent of $125 a month to maintain and repair communications equipment for front-line ISIS fighters.

Kuzu pleaded not guilty at the arraignment in Texas, according to Erin Dooley, a spokeswoman for the US Attorney's Office for the Northern District of Texas.

CNN has reached out for comment to the Federal Public Defender's Office in Dallas, which is representing Kuzu.

US officials familiar with the situation had told CNN earlier Thursday that the US government had transported Kuzu from Syria to face trial for his alleged involvement with the terror group.

The officials said Kuzu, who is a dual US-Turkish national, had been previously held by the US-backed Syrian Democratic Forces, a group of Kurdish-led anti-ISIS fighters.

2000 foreign ISIS fighters held in Syria

The SDF are currently holding over 2,000 foreign ISIS fighters from over 50 countries, a group that includes several hundred Europeans, according to one US official.

The US military helped facilitate the transfer.

The US government has long sought to encourage countries to repatriate their citizens, and the Department of Justice has been able to charge several American citizens for their alleged involvement with ISIS, including Rulan Asainov, who was repatriated last month. Asainov was arraigned in federal court in Brooklyn, New York, and charged with support to the terror group. He did not enter a plea at the arraignment.

"We now have 2,000 prisoners — ISIS prisoners. And we're telling Europe, 'Look, they were going to Europe.' They weren't coming here; they were going to Europe. You've got to take them," President Donald Trump said at a cabinet meeting last month.

"We can't be responsible for these people for 50 years or whatever it may be, or more and so we're negotiating with Europe, and we're negotiating with Iraq and lots of other people," Trump added.

However, the effort to get other countries to repatriate their citizens from SDF detention camps has had limited success to date with only seven countries -- the US, Italy, Kosovo, North Macedonia, Bosnia and Herzegovina, Kazakhstan and Morocco -- having publicly repatriated their fighters.

Some countries reluctant to repatriate fighters

Many countries are reluctant to repatriate their fighters because of the difficulty of prosecuting suspected ISIS members based on evidence collected on the battlefield.

The number of foreigners in detention increased sharply following the capture of ISIS' last area of territorial control in Baghouz, Syria, in late March. US officials told CNN in April that they were investigating reports that some of those detainees were US citizens.

The foreigners are among the more than 9,000 ISIS fighters being held by the SDF, with the majority of those being Syrian and Iraqi nationals. An additional 60,000 of what the US government refers to as ISIS "affiliates" are staying in makeshift camps where the SDF has a security presence.

Some have expressed concerns about the fate of these prisoners, particularly if the US were to withdraw its remaining troops from Syria.

Before this week, the United States had repatriated seven adults from Iraq and Syria who were associated with ISIS and criminally charged five of them, including Asainov and a Texas man in January, according to the Justice Department.

"The United States is leading by example. We've called on other countries to repatriate and prosecute. ... That's exactly what we've done," Ambassador Nathan Sales, the State Department's coordinator for counterterrorism, told reporters Thursday.

"The way to be tough on foreign terrorist fighters is to prosecute them. Right now they are not facing justice for the crimes they've committed, they are in temporary holding facilities, and we've seen a number of attempted jailbreaks -- the risk they could get out is not trivial," Sales said, urging Western European nations to take their citizens back.

Fifty-nine Americans are believed to have traveled overseas to join ISIS, and more than a dozen have faced terror-related charges after returning to the US voluntarily or through repatriation, according to research from the George Washington University Program on Extremism. Many more are believed to have died on the battlefield.

The US has repatriated eight adult US citizens from Iraq and Syria, including Kuzu. The Justice Department has brought criminal charges against six of them.

And while the number of foreigners traveling to Syria to join ISIS has decreased, officials have expressed concerns about the ability of other ISIS affiliates being able to attract foreign recruits.

Last month, the Department of Justice said that the FBI had arrested two men in Arizona after they checked in for a flight to Egypt, where the Justice Department alleges they intended to join ISIS.

This story has been updated.