LONDON (AP) — Multiple lines on the London Underground network were suspended or disrupted Monday because of a power outage, the British capital’s transport authority said.

The Transport for London website showed at least three subway lines were suspended and there were severe delays and partial suspensions on at least six other lines during the afternoon rush. By 11 p.m., service had mostly recovered with only one line experiencing severe delays.

The London Fire Brigade cited a brief fault on the National Grid’s transmission network.

Transport for London said trains were stopped temporarily due to the outage, and some stations were closed because it wasn’t safe for them to operate without power.

Last month, a power outage caused by a fire at an electrical substation in west London forced the closure of Heathrow Airport for almost a day, disrupting thousands of flights.

The government ordered an investigation into the country’s “energy resilience” after the fire, which raised concerns about the U.K.’s ability to withstand disasters or attacks on critical infrastructure.