More than a dozen voters had already cast ballots for a school district election inside a community center in Ankeny, Iowa, on Tuesday when a pair of dog walkers strolling through the parking lot spotted a suspicious-looking package.

When police responded, they found a live pipe bomb. The community center was evacuated and voting at the site was halted for several hours as specialists in heavy bomb suits carefully disarmed the device.

There’s no indication of who left the bomb or why, police said, and no other bombs have been found at other polling sites around the city of 45,000 people just outside Des Moines.

“The @AnkenyPolice did an excellent job today ensuring community safety,” said Jamie Fitzgerald, Polk County’s auditor and commissioner of elections. “There is no way of knowing how long this device had been at the Lakeside Center.”

In the lead-up to November’s elections, fears were heightened for the potential of violence at polling places nationwide as arsonists targeted some ballot drop-off boxes and statewide election officials faced bomb and death threats. Iowa leaders decried the incident in Ankeny.

“I’m deeply concerned to learn that a pipe bomb was found at a polling place in Ankeny earlier today,” Rep. Cindy Axne (D-Iowa) said on Twitter. “This threat to our elections in unacceptable, and those responsible should be held accountable for this attempted violence against our democracy and its citizens.”

The bomb was spotted outside the Lakeside Center in Ankeny around 9:30 a.m., police said in a statement. The building was being used as a polling center as voters weighed in on a special election to decide how the Ankeny Community School District should spend capital improvement funds, the Des Moines Register reported.

When police determined the device was a real bomb, a special unit from the Iowa State Fire Marshal Division was called in to disarm it, along with agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives and the FBI. Just before noon, they detonated the bomb to dispose of it.

The center opened back up for voting around 12:30, and Fitzgerald said his office helped anyone who showed up to vote during the police operation find a different polling center.

Paul Pate, Iowa’s secretary of state, thanked police for safely disarming the bomb.

“Great job today @Polkauditorfitz, poll workers, law enforcement & everyone involved with ensuring the safety of voters & the public,” Pate, a Republican, said on Twitter. “Thank you to all. True team effort.”