A natural gas company is working to restore service to thousands of customers in Colorado following vandalism that damaged lines and forced gas to be shut off, leaving residents without heat and hot water. 

According to a statement Monday from Black Hills Energy's vice president of operations, Vance Crocker, crews were working to bring more than 3,500 gas meters in Aspen back online, a process that “requires several steps."

“We must first make sure all gas meters are off, then purge the system so it’s ready for the reintroduction of the natural gas supply,” Crocker added. “Finally, our technicians will go door-to-door and relight each customer’s gas appliances.”

According to NBC’s Denver affiliate KUSA, Crocker said during a community meeting Monday that the process of restoring gas lines was expected to go into Tuesday, with 150 technicians deployed to work on the issue and 4,000 heaters being distributed during repairs. 

The Aspen Times reported that gas lines across the city were found damaged, with the name of environmental advocacy organization Earth First! written on one pipe at one of three Black Hills Energy sites vandalized.

It was not clear as of Monday whether the organization’s members were directly involved in the damages, according to the Aspen newspaper. 

“They would have had to have some familiarity with the system” to carry out the sabotage, Bill Linn, Aspen assistant police chief, said Monday. 

“They tampered with flow lines. They turned off gas lines,” he continued. 

Linn added that police have not received any communication from Earth First! in response to the damages. 

In Monday’s community meeting, Aspen Police Chief Richard Pryor said that a multijurisdictional investigation was being carried out to determine who was behind the vandalism and how they were able to carry it out.

Linn said Monday that the FBI was assisting local detectives in the investigation, as well as state law enforcement officials, according to the Times. 

Pitkin County Commissioner Patti Clapper, who was without heat Monday at her Smuggler Mountain-area home, called the vandalism "an act of terrorism." 

“It’s trying to destroy a mountain community at the height of the holiday season,” Clapper continued, the Times reported. “This wasn’t a national gas glitch. This was a purposeful act.”

Pitkin County Sheriff Joe DiSalvo said Monday that he was hesitant to characterize the incident as an attack. 

“I know that word has been thrown around a lot,” he said. “It’s not a word I would use,” instead calling the vandalism “an intentional act” to disrupt gas service to Aspen.