PHOENIX — Authorities discovered two suspicious letters today that were sent to the Phoenix office of U.S. Sen. Jeff Flake, prompting officials to evacuate part of the building as the nation is on high alert following similar incidents at other congressional offices and the explosions in Boston.

Tom Mangan, a spokesman for the Bureau of Alcohol Tobacco, Firearms and Explosives in Arizona, said Flake’s office called authorities this morning after the senator’s staff came across two suspicious letters. The letters were stained with an oily substance that’s believed to have caused irritation to the eyes and noses of two Flake staffers and a Phoenix police officer who responded to the scene, Mangan said.

Emergency crews in hazardous materials gear rushed to the scene and cleared out parts of the building, in the trendy Biltmore neighborhood of Phoenix. Sen. John McCain’s office is across the street, and staff there was told to be on the lookout for anything suspicious.

Police spokesman Tommy Thompson said authorities are trying to find out if the envelopes are dangerous. Mangan said he didn’t believe the letters had been opened.

The situation came a day after authorities said a letter containing ricin was mailed to the office of a Mississippi senator. The Secret Service also says it has intercepted a letter addressed to President Barack Obama that contained a substance that tested positive for the poisonous ricin.

Postal Inspection Service agents and technicians also were at the scene in Phoenix, spokesman Keith Moore said. He said he had no information on what had been found and didn’t know if the item or items had been sent through the mail.

Flake is a Republican who was elected to the Senate last year after serving in the U.S. House. He is among a bipartisan group of U.S. senators who worked on an immigration bill that was formally introduced in the Senate earlier today.