NEW YORK — A Manhattan college was briefly evacuated after a bomb threat. But no devices were found, and no one was injured.

Police say a Mercy College guard found a letter that said two bombs had been planted and were going to detonate at 6:30 p.m. The Manhattan campus occupies about two floors of a high-rise not far from the Empire State Building. It reopened at about 9 p.m.

No arrests have been made. Police say whoever wrote the letter said the school did not treat minorities well and that’s why the bombs were planted.

Mercy College is a private school based in Dobbs Ferry. It also has a satellite campus in the Bronx. About 10,000 undergraduate and graduate students attend the college’s campuses and there are about 210 faculty members.