ST. PAUL — A Minneapolis man was charged Friday with threatening law enforcement officials and writing on Twitter that a “massacre” would happen if authorities did not free six men who were arrested earlier this week and accused of trying to travel to Syria to join the Islamic State group.

According to an FBI affidavit, Mahamed Abukar Said used his Twitter account to threaten to kill a federal law enforcement official and demand that the men be freed. In one tweet on Wednesday, Said wrote, “the Feds are getting two choices. Either they gon free my bros or the gon have a massacre happen then they gon take me too,” the affidavit said.

Said also used Twitter to retaliate against a man who cooperated with authorities, the affidavit said, and posted a picture of the informant on Thursday.

Assistant U.S. Attorney Tracy Perzel said during Said’s initial court appearance Friday “these are very serious charges.” She said law enforcement officers have taken steps to ensure those who were threatened are protected.

Said is charged with one count of impeding and retaliating against a federal law enforcement officer and one count of using interstate communications to make threats to injure. He was detained pending a hearing Wednesday. His attorney, Shannon Elkins, did not immediately return a phone message left Friday by The Associated Press.

Said was arrested Friday afternoon, a day after a judge ordered detention for four of the six men who were charged with conspiracy to support a foreign terrorist organization. Authorities say the men were intent on going to Syria, even after many had been stopped from traveling previously.

The arrests of the six men, all of Somali descent, created tension in Minnesota’s Somali community, the largest in the United States. Since 2007, more than 22 young Somali men have traveled from Minnesota to Somalia to join the militant group al-Shabab. Authorities have also said a handful of Minnesota residents have traveled to Syria to fight with militants in the past year.

The six men were charged after a 10-month investigation that was aided by recordings made by a man who once planned to travel to Syria himself, but then decided to cooperate. Court testimony about the use of an informant, along with the judge’s decision to detain the men, prompted angry reaction from some of the roughly 200 local Somalis who attended Thursday’s hearing.

The FBI affidavit in Said’s case says that as Thursday’s hearing was nearing an end, Said tweeted a picture of the informant. A message with that picture contained profanity and called the man a “snitch.” The tweet was visible for a short time before it was removed.

Somali community advocate Omar Jamal said the charges against Said “send a very clear message to the community. They should take it serious.” He said young people need to let the case work through the court system.

The affidavit unsealed Friday also alleges Said communicated via Twitter with one of the men who is accused of trying to join ISIS, Guled Ali Omar. One of Omar’s brothers, Mohamed Ali Omar, has been convicted of threatening FBI agents who were investigating the case.

FBI Special Agent in Charge Richard Thornton said in a statement: “The FBI will not tolerate such threats against the U.S. government, witnesses, or the public at large, and will take swift action to eliminate such threats.” He said anyone who seeks to intimate others through threats will be prosecuted with the “full force of the law.”

Federal prosecutors from Wisconsin will handle Said’s case to avoid a potential conflict of interest.