WATERVILLE — An 18-year-old Waterville man who was arrested by the FBI earlier this month planned to use handmade explosive devices to commit “mass murder” at a mosque in Chicago, according to the United States Attorney’s Office for the District of Maine.

Xavier Pelkey was arrested Feb. 11 by federal agents at his Front Street apartment. He is to be held behind bars until his case goes to trial, according to Assistant U.S. Attorney Craig M. Wolff.

A date for Pelkey’s trial had yet to be set as of Thursday.

Two juveniles who were communicating online with Pelkey told FBI agents, in a now-sealed declaration, of Pelkey’s alleged plan to use explosives to “commit mass murder” at a Chicago mosque, Wolff said Tuesday at a detention hearing.

The declaration is expected to be unsealed at some point, Wolff said Thursday.

The Council on American-Islamic Relations, the country’s largest Muslim civil rights organization, issued a statement Wednesday calling for hate crime charges against Pelkey.

“This disturbing case highlights the real threat posed by anti-Muslim bigotry, antisemitism and other forms of hate,” Edward Ahmed Mitchell, the organization’s deputy director, said in the statement.

Pelkey is facing a federal charge of possessing unregistered destructive devices, punishable by up to 10 years in prison and a $10,000 fine.

FBI agents reportedly found three explosive devices at Pelkey’s apartment that investigators determined were fireworks bundled together with tape.

An FBI bomb technician who examined the devices found staples, pins and thumbtacks attached to them that the technician believed were meant as shrapnel when the devices were detonated, according to a federal criminal complaint.

Pelkey told federal agents who raided his apartment at 80 Front St. he taped the fireworks together because he wanted to make a “bigger boom,” according to the federal complaint. Pelkey did not respond to questions about why staples and other sharp objects were added to the fireworks, the complaint said.

Pelkey is being represented by Camden lawyer Christopher MacLean, who could not be reached Thursday for comment.