Federal prosecutors have charged a Brazilian man living in the US illegally with sending a letter to immigration authorities warning of an armed attack on a Boston school.

Clebio De Lima, who lives in the Boston suburb of Quincy, was charged on Thursday with making false statements to federal authorities.

The US attorney says US Citizenship and Immigration Services offices in Boston received an unsigned letter handwritten in Portuguese last February that said a man named Mario had purchased two guns and was planning an attack on the school.

It was determined that the allegations in the letter were false.

During an interview with agents in September, the 43-year-old De Lima denied any knowledge of the letter.

His public defender did not return a message for comment.