MINNEAPOLIS — U.S. authorities have charged six Somali-American men from Minnesota with planning to join Islamic State and fight for the militant group in Syria, the U.S. attorney for Minnesota said Monday.

The six, all U.S. citizens, were part of a larger group of friends and relatives who had been conspiring for the past 10 months, many trying multiple times to leave the country, federal prosecutors alleged.

Their arrests Sunday capped a yearlong FBI investigation into would-be Islamic State recruits seeking to journey abroad, and there was no evidence the accused had plans to carry out any attacks inside the United States, prosecutors said.

Dozens of people from the Minneapolis-St. Paul area, many of them young Somali-American men, have traveled or attempted to travel overseas to support Islamic State or al Shabaab, a Somalia-based militant group, since 2007, according to U.S. prosecutors.

“We have a terror recruiting problem in Minnesota,” U.S. Attorney for Minnesota Andrew Luger told a news conference.

Four men — Zacharia Yusuf Abdurahman, 19; Adnan Farah, 19; Hanad Mustafe Musse, 19; and Guled Ali Omar, 20 — were arrested in Minneapolis. They appeared for a brief hearing in federal court Monday and were held pending a detention hearing scheduled for Thursday.

Abdurahman Yasin Daud, 21, and Mohamed Abdihamid Farah, 21, were arrested in California after driving from Minneapolis to San Diego. They, too, were ordered by a judge to remain jailed without bond until their detention hearings, which were slated for Friday. Extradition proceedings to return them to Minnesota were set to begin on April 30.

Three of the accused had traveled to New York by bus with another man, Hamza Ahmed, in November, when they were stopped from boarding international flights with the intent of reaching Syria, prosecutors said.

Ahmed was indicted in February on charges of conspiring to support Islamic State and lying to federal agents investigating recruitment by militant groups.

The group met regularly to plan trips, prosecutors said. One unidentified member had doubts, changed his mind and recorded their meetings, Luger said.

“These were focused men who were intent on joining a terrorist organization by any means possible,” Luger said.

They received advice and encouragement from another group member, Abdi Nur, who has stayed in contact with them since he left the United States last year and joined Islamic State in Syria, prosecutors said. Nur was charged in November.