WASHINGTON, D.C.—The U.S. Justice Department has received more than 400 fraud complaints involving relief aid after Hurricanes Harvey and Irma and expects a spike in fraud complaints in the coming months, department officials said on Thursday.

The majority of fraud efforts target the federal government itself as people try to defraud the Federal Emergency Management Agency (FEMA), which administers disaster relief, said Corey Amundson, acting director of the department’s National Center for Disaster Fraud.

“The fraudsters aren’t waiting. They need to know we’re coming for them and the public needs to be informed,” Amundson told reporters. “We find it despicable that people that have already been victimized by these disasters face the daunting prospect of being victimized a second time.”

Among complaints are accounts of people impersonating FEMA representatives, charity fraud, suspicious ads, Red Cross donation fraud, electricity disconnection threats and thieves pretending to need shelter, Amundson told reporters.

The complaints come from around the country, not just areas affected by the storms, Amundson, who is the acting U.S. attorney for the Middle District of Louisiana, said in a conference call with his counterparts for Puerto Rico and Florida.

The Center for Disaster Fraud, which was created after Hurricane Katrina in 2005 to handle fraud complaints, has set up a toll-free number (866-720-5721) for people to report suspected abuses.

U.S. attorneys offices in Florida and Puerto Rico also announced task forces of state, local and federal agencies to fight storm-related illegal activity.

Amundson did not have dollar estimates for fraud related to Katrina or an estimate any for Hurricanes Harvey and Irma, which ravaged Texas and the southeastern United States as well as the U.S. Virgin Islands and Puerto Rico.

He said it can take years for fraudulent disaster aid claims to be identified and detected as they work through the federal system.