LONDON — In the aftermath of Britain’s deadliest fire in decades, two senior officials sought to deflect blame from the government over the weekend by arguing that the type of building material believed to have spread flames rapidly up the 24-story Grenfell Tower had been banned under national fire safety regulations.

But experts on British fire safety rules say that the material, used as exterior cladding, in fact complied with regulations. Other countries, including the United States, have placed stricter restrictions on how such materials can be used, but Britain had not yet done so, they said.

The question of whether the cladding complied with national regulations — and whether those regulations were too lax — is a central part of the investigation into the horrific blaze last week. It will help determine how much blame falls on the government, and how much is assigned to the tower’s owners or builders.

The toll rose on Monday to 79 confirmed or presumed dead and was expected to climb further, making the fire the country’s deadliest in decades, perhaps since the early 20th century. It broke out at the West London tower early on Wednesday, lasted six hours and incinerated the building. Hundreds were left homeless. The government has announced a formal public inquiry, and a criminal investigation has been opened.