A package that officials said contained two vials of a "homemade explosive substance" was discovered near the Arizona State Capitol in downtown Phoenix on Monday.
Federal authorities are investigating suspicious letters sent to election offices in five states.
A series of threatening letters containing a mysterious white powder is raising concerns that Republican lawmakers in Kansas are being targeted.
Since Friday, about 100 letters have been received by Kansas GOP lawmakers and Kansas Attorney General Kris Kobach, who is also a Republican, officials said.
The number more than triples the amount when the situation was first reported early Friday evening.
More than 30 such letters have been reported across the state as of 4 p.m. Friday, the Kansas Bureau of Investigation said.