Six people were arrested Sunday in Minneapolis and San Diego in an alleged ISIS-related plot. Youths play basketball before the start of a solidarity rally by the Minneapolis Somali community to denounce al-Shabab's attack of a shopping mall in Nairobi, in Minneapolis on Sept. 27, 2013. Reuters/Eric Miller

Federal agents Sunday arrested at least six people in Minneapolis and San Diego in what was described as an ISIS-related terror plot. Minneapolis U.S. Attorney Andrew Luger told Minnesota Public Radio nearly simultaneous arrests were made in the two cities.

The report quoted a Somali woman in Minneapolis as saying she was the mother of two of those arrested. She said agents showed up at her house around noon, arresting the son who was home and seizing a tablet belonging to the other son, who was arrested in San Diego. A second Somali woman said her son was arrested in Minneapolis shortly after returning home from work.

Family members said they do not know why the six men were arrested, and a Luger spokesman declined to release further details. A news conference was scheduled for Monday morning.

“There is no threat to public safety,” Luger spokesman Ben Petok told the Minneapolis Star Tribune.

Somali activist Omar Jamal said the Somali community in Minneapolis is confused. "This is a very serious issue," he said. "We as a community are concerned about losing our kids to ISIS.”

The MPR report said investigators have been looking into 15 young residents of the Minneapolis-St. Paul area who traveled to Syria to support the Islamic State group in the past year.

Earlier this month, a Kansas man was charged with planning to detonate a bomb at Fort Riley in support of the Islamic State group. Two women were arrested in New York for allegedly plotting to set off a bomb in the New York area after being radicalized by the Islamic State group.

In March, two suburban Chicago men were arrested in an alleged plot to blow up the Illinois National Guard armory in Joliet. One of the men, who was a member of the National Guard, had planned to join the Islamic State group in Syria and allegedly gave the second man, his cousin, the information he would need to get into the armory to plant the explosives.