Police are checking the authenticity of an inland letter reportedly written by the People's War containing a threat to kill Andhra Pradesh Chief Minister N Chandrababu Naidu, who was injured in an attack by the naxalite outfit on October 1.

In the letter sent to the office of Chittoor district superintendent of police, the outfit has reportedly warned Naidu that "we will target you within one month", police sources said.

They said the letter has been faxed to police headquarters in Hyderabad.

There are doubts about the authenticity of the unsigned letter, as the PW normally uses its letterhead, the sources said.