ST. PAUL, Minn. » Six people were arrested Sunday in connection with a terrorism investigation in Minnesota, where authorities have been tracking youths who have traveled or tried to travel to Syria to fight with militants, including the Islamic State group, authorities said.

A spokesman for the Minnesota U.S. Attorney’s Office said the arrests were made in Minneapolis and San Diego but there is no threat to public safety. Spokesman Ben Petok did not give details about the charges. He said more information would be released Monday.

The U.S. Attorney’s Office and the FBI planned a news conference Monday to announce details. The news conference was billed in a press release as an announcement of a joint terrorism task force operation.

Kyle Loven, spokesman for the Minneapolis office of the FBI, said six people were arrested Sunday but gave no further details. An FBI spokesman in San Diego referred questions to Loven.

Authorities say a handful of Minnesota residents have traveled to Syria to fight with militants within the last year. At least one Minnesotan has died while fighting for the Islamic State.

Since 2007, more than 22 young Somali men have also traveled from Minnesota to Somalia to join the terrorist group al-Shabab.

Four Minnesotans have already been charged in connection with supporting terror groups in Syria, including the Islamic State group.

One man, 19-year-old Hamza Ahmed, had been stopped at a New York City airport in November as he and three others were attempting to travel to Syria. Ahmed has been indicted on charges of lying to the FBI during a terrorism investigation, conspiring to provide material support to the Islamic State group, and attempting to provide material support. He has pleaded not guilty.

But there have been no public charges filed against his three companions, and little information had been released about them. An FBI affidavit said they are all between the ages of 19 and 20 and live in the Twin Cities.