OMAHA, Neb. — The FBI and law enforcement agencies around Omaha have teamed over a rash of bank robberies officials believe have street gang ties.

Officials held a news conference Tuesday at the FBI field office in Omaha to announce the task force. Randall Thysse, special agent in charge of the FBI’s Omaha office, says officials are particularly concerned about the violent nature of recent bank robberies around Omaha and Council Bluffs, Iowa. Thysse says of the 42 armed bank robberies in the last 17 months, 33 were similar enough that investigators believe they are related.

Thysse says the robbers storm banks with guns drawn, their faces covered and yelling demands. In at least one case, a teller was bound.

Omaha Crime Stoppers has doubled its reward for information on the bank robberies to $20,000.