TACOMA — A fourth electrical substation was vandalized late on Christmas Day in Washington, leaving homes in Kapowsin and Graham temporarily without power, according to the Pierce County Sheriff’s Office.

By 7 a.m. Monday, more than 10,500 Puget Sound Energy customers were without electricity in the region, KOMO-TV reported.

The suspects broke into a fenced area and vandalized equipment, causing a fire, officials said. The fire was extinguished and power was later restored, but no suspects are in custody, officials said.

The attacks come as federal officials are warning that the U.S. power grid needs better security to prevent domestic terrorism and after a large outage in North Carolina earlier this month that took days to repair.

The first substation was vandalized at about 5:30 a.m. Sunday, followed by a second substation, according to Tacoma Public Utilities. The outages affected about 7,300 customers in an area southeast of Tacoma. Just before noon, the utility had restored power to all but 2,700 customers whose power was estimated to be restored at about 6:30 p.m. Sunday.

Meanwhile, just before noon, Puget Sound Energy reported vandalism that had happened at about 2:30 a.m. Sunday caused a power outage at one of its substations. The nearly 7,700 customers who lost power had it restored by 5 a.m., Puget Sound spokesperson Andrew Padula said. The company is investigating, along with authorities, and declined to comment further, according to Padula.

In all four cases, the sheriff’s office says someone forced their way into the fenced area surrounding the substations and damaged equipment to cause a power outage.

Power stations have been hit in Washington and Oregon in the last month.

Portland General Electric, the Bonneville Power Administration, Cowlitz County Public Utility District and Puget Sound Energy confirmed six separate attacks on electrical substations in Washington and Oregon in the previous weeks, according to Oregon Public Broadcasting and KUOW-FM in Seattle.