Brazil's federal police say a bomb threat forced a passenger plane to make an unplanned landing in the Amazon city of Manaus.

Federal police in Manaus said a TAM Airlines flight took off from Brasilia Saturday morning and was en route to the city of Boa Vista.

A note left in a bathroom in Brasilia's airport claimed that a bomb was aboard the TAM jet. It had already taken off when the note was discovered, so officials routed the plane to Manaus, where it safely landed.

Authorities said a search of the plane has yet to turn up any device. But the jet remains on the tarmac in Manaus while an investigation continues.

A federal police official in Manaus said no arrests have been made.