The building serves as Democratic headquarters for both the state and Maricopa county, which is Arizona’s most populous county and the most populated county in a swing state.

Maricopa County Democratic Party Communications Director Edder Diaz-Martinez confirmed to Newsweek that investigators had reached out to the party and informed them that the fire was caused by arson.

“We can confirm that it was arson,” Diaz-Martinez said. “The investigation is ongoing. We’re shocked, stunned and saddened that it came to something like this. It’s a complete act of terrorism.”

Diaz-Martinez said that the northern part of the building, which housed county headquarters, was destroyed.

“It looks like, from what I’ve heard from authorities, the fire started on the north side of the building and the county party side is completely gone,” Diaz-Martinez said.

Firefighters arrived at the scene around 1 a.m., after receiving reports of smoke near the building. They confirmed that the building was unoccupied and were able to eventually extinguish the fire. No injuries were reported.

Investigators were able to confirm the fire was deliberate relatively quickly, having told Democrats they were investigating the fire as a possible arson earlier on Friday, but a determination could take several weeks.

The fire happened one day before the party was planning a large virtual convention. Diaz-Martinez noted that it also happened shortly after it was announced that two controversial Confederate monuments were being removed from the state Capitol complex in Phoenix.

Although November’s election is less than 100 days away, the building had recently been used sparingly due to the COVID-19 pandemic, with staff instead working remotely since mid-March. However, party officials said the building held significant sentimental value.

“Our organization has worked out of this building for over a decade,” Steven Slugocki, a party chairman, said in a statement. “It has been home to thousands of volunteers, candidates, supporters and friends. Memories were made, victories were celebrated, and lifelong friendships have been forged.”

Despite the attack on their headquarters, Diaz-Martinez said Democrats remain focused on working in preparation for the upcoming November election. Polling has indicated they could be on course to make gains in the traditionally Republican-leaning swing state.

“Our work is just going to continue, this isn’t going to deter anything that we’ve set in motion. We are continuing to build momentum,” he said. “But for this kind of thing to happen right at the brink of when we’re about to flip the state is just incredible.”

President Donald Trump won the state by 3.5 percent in 2016 but recent polls have shown him consistently trailing former Vice President Joe Biden. The last Democrat to win a presidential election in Arizona was former President Bill Clinton in 1996.

Democrats could also be poised to pick up a seat in the U.S. Senate, with Mark Kelly, an astronaut and the husband of former Rep. Gabby Giffords, maintaining a double-digit lead over Republican Senator Martha McSally.

Correction 7/28, 4:08 p.m.: This article has been updated to correct the title of Edder Diaz-Martinez, who is the communications director for the Maricopa County Democratic Party, not the Arizona Democratic Party.