Arizona’s Republican gubernatorial candidate Kari Lake closed a campaign office after an envelope containing “suspicious white powder” was delivered to the premises on Saturday, according to reports.

A member of the candidate’s staff unwittingly opened the envelope and is now under “medical supervision”, campaign spokesperson Colton Duncan told CNN.

The FBI will analyze the item at its laboratory in Virginia, and agents stopped short of saying whether they had confirmed the powder was harmful.

“It was one of two envelopes that were confiscated by law enforcement and sent to professionals at Quantico for examination, and we are awaiting details,” Duncan reportedly said.

While Lake was taking the threat seriously, Duncan said, she would not be deterred. “In the meantime, know that our resolve has never been higher, and we cannot be intimidated,” Duncan added. “We continue to push full speed ahead to win this election.”

Katie Hobbs, Arizona’s Democratic secretary of state and Lake’s opponent in Tuesday’s election, decried the incident. “The reported incident at Kari Lake’s campaign office is incredibly concerning and I am thankful that she and her staff were not harmed,” Hobbs’ campaign reportedly commented. “Political violence, threats, or intimidation have no place in our democracy. I strongly condemn this threatening behavior directed at Lake and her staff.”

This case ensnaring Lake’s office comes amid heightened concerns about political violence surrounding the 2022 midterm elections Tuesday and unrest generally. Paul Pelosi, Nancy Pelosi’s husband, was bludgeoned by a hammer-wielding home intruder on 28 October in an attack that authorities described as politically motivated.

In June, California resident Nicholas John Roske was arrested near US supreme court justice Brett Kavanaugh’s Maryland home for allegedly trying to kill the jurist. Roske, who has pleaded not guilty, allegedly told a police officer that he was angry over the then draft supreme court opinion overturning the federal abortion rights established by the landmark Roe v Wade case.

Threats against politicians have surged in recent years, with the US Capitol police saying that they investigated 9,625 threats against legislators in 2021, which began with supporters of Donald Trump launching an attack on the congressional session that certified the former president’s defeat to Joe Biden. That toll was about a threefold increase from 2017, Capitol police said.

While US House members will now receive a $10,000 security allowance, the stipend has been criticized as insufficient.

The New York police department (NYPD) warned on 27 October that extremists might target political events and polling sites in advance of Tuesday’s race.

A New York City voting site was shuttered for several hours Sunday after a bomb threat, authorities said. The threat was reportedly directed toward the school which housed the site.

The NYPD said this threat was neither against the polling station nor politically motivated.