A Norwegian man was arrested on Wednesday after sending emails threatening to kill police in Maine with explosives and high-powered rifles, officials said.
Police departments across the United States are on high alert following attacks in Dallas and Baton Rouge last month that killed eight police officers.
Portland police said in a statement that Espen Brungodt, 28, sent the threats to the Portland Police Department and local media outlets around 8:45 a.m. on Wednesday and was arrested unarmed and without incident roughly four hours later.
Police said Brungodt entered the United States on July 26 through Boston and was traveling with family members.
The Portland Press Herald newspaper published online a copy of the email it had received from Brungodt, which stated in part: "Time for more police to die."