Notre-Dame cathedral in Paris is still at risk of collapse after being gutted by a fire in April, with more stonework falling during the recent heatwave in the French capital, the government said on Wednesday.
France's culture ministry insisted that the urgent need to make the cathedral safe had dictated the pace of the works, following criticism that it had ignored the risks of lead poisoning.
Work to secure the cathedral was suspended on July 25 to allow for decontamination of the lead that had spread during the fire. The work should resume next week.
The culture ministry said that in the aftermath of the fire all work on the cathedral had been aimed at avoiding its collapse, and had not yet involved any kind of restoration.
"There were recently new falls of stones from the nave vaults due to the heatwave," it said.
"It is only the urgency linked to the persistent risk of a collapse that justifies the rhythm of work undertaken" since the fire.
French investigative news site Mediapart published a report this week accusing the ministry of repeatedly ignoring warnings by labour inspectors about the dangers posed by the lead until the works were finally suspended on July 25.
But the ministry rejected Mediapart's allegations that it had failed to pay attention to the risks encountered by workers on the site.
"All the state services involved at the site have made the health of the workers the absolute priority, above all other consideration," it said.
President Emmanuel Macron has set an ambitious target of five years for the restoration to be finished. But the ministry said restoration work would not even begin until next year.
"The first restoration works will not take place -- at the very earliest -- before the first half of 2020," it said.
Hundreds of tonnes of lead in the roof and steeple melted during the April 15 blaze that nearly destroyed the gothic masterpiece, with winds spreading the particles well beyond the church's grounds.
Paris prosecutors said in June that a poorly stubbed-out cigarette or an electrical fault could have started the fire and opened an investigation into criminal negligence, without targeting any individual.