Britain’s counterterrorism police are leading the investigation into the cause of the fire near Heathrow Airport, signaling that the possibility of sabotage was being taken seriously, at least as a precaution. But officials said there was no immediate evidence that foul play was involved.

After the blaze at the electrical substation and subsequent power outage, the scale of the resulting chaos raised uncomfortable questions for Britain’s government about the security measures protecting key transport hubs and the resilience of the country’s aging infrastructure.

The Metropolitan Police in London said that counterterrorism specialists had taken charge “given the location of the substation and the impact this incident has had on critical national infrastructure.”

Sadiq Khan, the mayor of London, said it was “not unusual” for the specialized officers to be involved in an investigation of such a major incident, and he told Sky News that there was “no reason at all for anyone to be concerned or alarmed.”

With the fire under control but still burning, nonetheless, nothing has been ruled out.

In a statement, Prime Minister Keir Starmer said he was “receiving regular updates” about the situation at Heathrow and was “in close contact with partners on the ground.” He added that he knew the outage was “causing distress and disruption, especially for those traveling or without power in their homes.”

A spokeswoman for Heathrow said on Friday afternoon that some flights would resume later in the day, adding that officials hoped the airport would be fully operational by Saturday.

John McDonnell, a lawmaker who represents Hayes, the area where the fire broke out, said on Friday afternoon that any investigation would need to look at “why backup arrangements have not worked” and how the infrastructure could be so vulnerable.

“There are lessons that have got to be learned here,” he told reporters.