DENVER (Reuters) - Anonymous notes threatening to “blow up” a refugee community center catering mainly to Muslim immigrants were found at the Denver-area building, prompting a hate-crime investigation by the FBI, police said on Friday.

The two identical, typewritten notes were left on Thursday in the parking lot and stairwell of the Mango House in the Denver suburb of Aurora, both with the message: “WERE GONNA BLOW UP ALL OF YOU REFUGEES,” according to police spokesman Sergeant Chris Amsler.

The threat surfaced amid heightened consternation in the Muslim-American community over an executive order signed on Friday by President Donald Trump to limit the flow of immigrants and refugees from some predominantly Muslim countries into the United States.

Police evacuated and checked the refugee center in Aurora after the notes were discovered but found no signs of explosives or other suspicious devices and have not identified any suspects, Amsler told Reuters.

“This is an ongoing investigation and is a top priority for us,” Amsler said. “We don’t tolerate that type of thing in the city of Aurora.”

The Federal Bureau of Investigation office in Denver declined comment, but Amsler said, “The FBI is now assisting us in our efforts to solve this bias-motivated crime.”

Dr. P.J. Parmar, a physician who runs a general medical practice inside the building that serves refugees in the Denver metropolitan area, said he treats patients from a number of war-torn countries, primarily from Africa and the Middle East.

He called the anonymous threats “unfortunate,” but said, “It hasn’t changed what we do, and we’re still seeing patients.”

The building also houses tenants who provide language and citizenship classes, a food bank and other resettlement services to political refugees.

A spokesman for the Washington-based Council for Islamic-American Relations (CAIR) said the threats were especially egregious for targeting a vulnerable population.

“Those fleeing violence and persecution must be welcomed and supported, not targeted by hate,” Ibrahim Hooper said in a statement. “State and federal law enforcement authorities should treat this as a terroristic threat and act accordingly.”

Parmar said he believed it was no coincidence that such a threat coincided with the president’s moves to curb the flow of refugees into the country.

“There’s always been xenophobic element in society, but now they have a voice that allows them to come out of the shadows,” he said.