PHOENIX » Authorities are investigating two suspicious letters that were sent to the Phoenix office of U.S. Sen. Jeff Flake of Arizona.

Emergency crews in hazardous materials gear were seen outside the building.

U.S. Sen. John McCain has an office directly across the street, and a spokesman for him said authorities have told staff not to open any packages as authorities investigate.

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 suspicious substance.

Flake is a Republican who was elected to the Senate last year.