LONDON -- British police increased the number of people killed or presumed dead in the London high-rise fire disaster to 80, saying Wednesday that a final death toll may not be known until the end of the year.

Most of those killed in the June 14 inferno at Grenfell Tower were believed to be from just 23 of the building's 129 apartments, said Fiona McCormack, a Scotland Yard detective superintendent. The previous figure of people believed to have died in the fire was 79.

Authorities were urgently testing cladding fixed to scores of high-rise towers across Britain in the wake of the blaze, which is believed to have spread so rapidly because of flammable external panels.

Prime Minister Theresa May said that 120 high-rise buildings in 37 parts of Britain have failed fire-safety tests so far -- a 100-percent failure rate.

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The tragedy has prompted hard questions about building regulation and fire safety, and political leaders have traded accusations about who is to blame. Labour Party leader Jeremy Corbyn said Wednesday that it showed "the terrible consequences of deregulation and cutting corners."

But May said "there is a very wide issue here" that can't be pinned on any single government.