At least 15 US governors have received letters rigged to catch fire when the envelope was opened,and investigators on Friday questioned inmates at a Nevada prison over the letters, media reports said.

The mailings, under investigation by the Federal Bureau of Investigation (FBI) and the Department of Homeland Security, bore a return address that named two inmates at the maximum-security Ely State Prison in Nevada.

Aides to several governors said they had been told by the FBI that the case was being treated as one of domestic terrorism, the reports said.

In three cases, a match inside the envelope flared when the letter was opened.

No one has been injured, although 23 staff members in the office of Governor Judy Martz of Montana were evacuated on Thursday after one of them opened the envelop sent there. The envelop ignited briefly and then petered out, a spokesman for the governor was quoted as saying.

The governors whose staffs confirmed receiving the suspicious letters by Friday afternoon included 11 Republicans and four Democrats, the reports said.

Source: Xinhua