By KIMBERLEE KRUESI, MICHAEL BALSAMO and ERIC TUCKER, The Associated Press

NASHVILLE, Tenn. — Sweeping communications outages continued to plague large swaths of Tennessee on Saturday as federal investigators combed the site for clues into the explosion of a recreational vehicle that rocked sleepy downtown Nashville on Christmas.

Police emergency systems in Tennessee, Kentucky and Alabama, as well as Nashville’s COVID-19 community hotline and a handful of hospital systems, remained out of service due to an AT&T central office being affected by the blast. The building contained a telephone exchange, with network equipment in it — but the company has declined to say exactly how many people have been impacted.

Meanwhile, investigators shutdown the heart of downtown Nashville’s tourist scene – an area packed with honky-tonks, restaurants and shops – as they shuffled through broken glass and damaged buildings to learn more about the explosion. While authorities are certain that this was a deliberate act, they have been mum on saying publicly who did this and why.

Mayor John Cooper has enforced a curfew in the downtown area until Sunday via executive order to limit public access to the area.

AT&T said restoration efforts are facing several challenges, which include a fire that “reignited overnight and led to the evacuation of the building.” This has forced their teams to work with safety and structural engineers and drilling access holes into the building in order to reconnect power.

“Our teams continue to work around the clock on recovery efforts from yesterday morning’s explosion in Nashville,” the company said in a Saturday statement. “We have two portable cell sites operating in downtown Nashville with numerous additional portable sites being deployed in the Nashville area and in the region.”

Gov. Bill Lee asked the White House on Saturday for federal assistance due to the “severity and magnitude” of the explosion’s impact. At least 41 buildings were damaged, and communications systems — including residential and cell phone service and 911 call centers — failed across the state, he said. Kentucky and northern Alabama were also affected, he said.

Ray Neville, president of technology at T-Mobile, said on Twitter that service disruptions affected Louisville, Nashville, Knoxville, Birmingham and Atlanta. “We continue to see service interruptions in these areas following yesterday’s explosion. Restoration efforts continue around the clock & we will keep you updated on progress,” he said in a tweet Saturday.

The outages had even briefly grounded flights at the Nashville International Airport, but service was continuing normally as of Saturday. The Federal Aviation Association has since issued a temporary flight restriction around the airport, requiring pilots to follow strict procedures until Dec. 30.

According to Metro Nashville Police Chief John Drake, police officers responded on Friday to a report of shots fired when they encountered the RV blaring a recorded warning that a bomb would detonate in 15 minutes. Police evacuated nearby buildings and called in the bomb squad. The RV exploded shortly afterward.

Law enforcement officials have said they believe the blast was intentional but don’t yet know a motive or target.

“This morning I toured the site of the bombing,” Gov. Bill Lee tweeted Saturday. “The damage is shocking and it is a miracle that no residents were killed. (First lady Maria) and I continue to pray for those who sustained injuries from the blast.”

Lee had been in quarantine due to his wife contracting COVID-19. However, the Republican said that he and Maria had both tested negative, allowing the two to visit downtown Nashville. Lee said the first lady had “fully recovered.”

The Federal Emergency Management Agency said in a report Saturday that tissue samples found at the scene were determined to be human remains.

Three people taken to area hospitals for treatment were in stable condition Friday evening.

The FBI has taken the lead in the investigation, agency spokesman Joel Siskovic said. Federal investigators from the Bureau of Alcohol, Tobacco, Firearms and Explosives are also involved in the investigation. The FBI is the primary law enforcement agency responsible for investigating federal crimes, such as explosives violations and acts of terrorism.

In West Virginia, a hospital system said Saturday that it was experiencing network connection issues directly related to the Nashville explosion. South Charleston-based Thomas Health, which operates two hospitals, said on its Facebook page that it didn’t have an estimated time of restoration.

Similarly, Sumner Regional Medical Center in Gallatin, Tennessee, said on its Facebook page that it was operating without access to some of its systems, including medical records.

“We prepare for situations like this and moved immediately to paper records. There has been no disruption to the delivery of patient care, and no cause for concern for this temporary issue,” the center said in a post Friday.

Associated Press writer John Raby contributed to this report from Charleston, West Virginia.