By Teresa Carson

PORTLAND, Oregon (Reuters) - Emergency officials were investigating two envelopes containing white powder and marked "anthrax" found in Portland, Oregon, on Wednesday, one at a downtown Hilton hotel and the other at an airport.

Preliminary tests on the envelope from the Portland International Airport found nothing dangerous, according to fire department spokesman Paul Corah. Airport offices were evacuated, but operations at the airport were not disrupted, he said.

Results of tests on the envelope found at the Hilton are expected later Wednesday evening. Offices at the Hilton were evacuated, but not the hotel.

Earlier in the week, a similar envelope was found in offices of Portland's Lloyd Center shopping mall. That envelope was found to contain benign material. Corah said he did not know if the incidents were related.

He said he did not know if the letters were sent through the U.S. Mail.

The Federal Bureau of Investigation is looking into the incidents, spokeswoman Beth Anne Steele, FBI said.

Last month, a Vancouver, Washington, nurse pleaded not guilty to charges that he sent more than 100 threatening letters containing a benign substance to members of Congress and the news media in February.

That incident set off the largest postal security scare in the U.S. capital since deadly anthrax-laced letters were discovered by several news organizations and U.S. Senate offices in 2001. Five people were killed and 17 sickened by those letters.

(Reporting by Teresa Carson; Editing by Mary Wisniewski and Philip Barbara)