An American who was captured in Syria and brought to the United States has been charged with providing support to ISIS.

Warren Christopher Clark, 34, of Sugar Land, Texas, appeared before a federal court judge in Houston on Friday, the Department of Justice said.

It said Clark, a convert to Islam, was charged in an indictment unsealed on Friday with providing material support to the Islamist miitant group – which Washington has designated as a foreign terrorist organization.

The Justice Department said Clark was captured in Syria by the Syrian Democratic Forces, an anti-ISIS alliance of Kurds and Arabs, and transferred to American custody this week.

“The arm of American Justice has a lengthy reach,” US Attorney Ryan Patrick said in a statement.

“The FBI continues to aggressively pursue individuals who attempt to join the ranks of [ISIS’s] foreign fighters or try to provide support for other terrorist organizations,” FBI agent Perrye Turner said.

If convicted, Clark, a former substitute school teacher, could face 20 years in prison.

In an interview with NBC News before his transfer to the United States, Clark said he went to Syria to become an English teacher for ISIS and was never a combatant.

“I wanted to go see exactly what the group was about, and what they were doing,” said Clark, also known as Abu Muhammad al-Ameriki.

He told NBC he crossed into Syria from Turkey in 2015.

– with reporting by Agence France-Presse