The death toll in the coal mine explosion and fire in western Turkey — the worst mine disaster to have occurred in the country — has increased to 282 on Wednesday, said a Turkish Minister.

Anti-government protests broke out in the mining town of Soma, as well as Istanbul and the capital, Ankara, with Prime Minister Recep Tayyip Erdogan being heckled as he tried to show concern.

The display of anger could have significant repercussions for the Turkish leader, who is widely expected to run for president in the August election, although he is yet to announce his candidacy.

Tensions were high as hundreds of relatives and miners jostled outside the mine’s entrance on Wednesday, waiting for news amidst a heavy police presence.

Energy Minister Taner Yildiz had earlier said that 787 people were inside the coal mine at the time of Tuesday’s explosion, and 363 of the miners had been rescued.

The death toll topped a 1992 gas explosion that killed 263 workers near Turkey’s Black Sea port of Zonguldak. It also left 150 miners still unaccounted for.

Mr. Yildiz said rescue workers were trying late on Wednesday to reach the bodies of up to 22 people trapped in one zone. Some of the workers were 1,400 feet deep inside the mine, he said.

One rescue worker who declined to be named said he led a ten-man team about half a mile down into the mine’s tunnels, where they recovered three bodies before being forced to flee because of smoke from burning coal. Rescue operations were halted for several hours on Thursday morning because high gas concentrations in the mine needed to be cleared.

Mr. Erdogan declared three days of national mourning and postponed a trip to Albania to visit the mine. He warned that some radical groups would try to use the disaster to discredit his government.

“Our hope is that, God willing, they will be brought out,” Mr. Erdogan said of those still trapped. “That is what we are waiting for.”

At a news conference, he tried to deflect a question about who was responsible for the disaster, saying, “These types of things in mines happen all the time.”

“These are ordinary things. There is a thing in literature called ‘work accident’. It happens in other work places, too. It happened here. It’s in its nature. It’s not possible for there to be no accidents in mines. Of course we were deeply pained by the extent here,” he said.

In downtown Soma, protesters, most in their teens and 20s, faced off against riot police in front of the ruling NKP party headquarters, smashing its windows with rocks.

Mr. Erdogan has been dogged by corruption allegations and was forced to oust four government ministers in December after they were implicated in a police-bribery probe. The scandal deepened after audio recordings were posted on the Internet suggesting corruption by the Prime Minister and his family members. Mr. Erdogan has denied the allegations and said they were a plot to discredit his government.

In Istanbul, hundreds of demonstrators gathered outside the headquarters of Soma Komur Isletmeleri AS — which owns the mine. Police used tear gas and water cannons to break up a group who tried to march to Istanbul’s iconic Taksim Square to denounce poor safety conditions.

Police also dispersed a group marching to the Energy Ministry in Ankara to protest the deaths.

Fences were erected and police stood guard outside Soma’s hospital, where scores of the injured were being treated. Some residents said the men were being pressured by the mining company not to talk about the blast.

Authorities said the disaster followed an explosion and fire at a power distribution unit and most deaths were caused by carbon monoxide poisoning. Mr. Erdogan promised the tragedy would be investigated to its “smallest detail” and that “no negligence will be ignored.”

Turkey’s Labor and Social Security Ministry said the mine had been inspected five times since 2012, most recently in March, and that no safety violations were detected. But the country’s main opposition party said Mr. Erdogan’s ruling party had recently voted down a proposal to hold a parliamentary inquiry into a series of small-scale accidents at the mines around Soma.

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A list of some recent fatal mine disasters around the world:

2013- 83 workers are buried by a massive landslide at a gold mining site in a mountainous area of Tibet, east of Lhasa, according to Chinese state media.

2012- At least 60 people dead after a landslide at a gold mine in a remote corner of northeast Congo.

2011- Fifty-two people are feared dead in southwestern Pakistan after a gas explosion deep in a coal mine in Sorange, near Quetta.

2010- 29 men are killed in New Zealand’s worst mining disaster in decades after a huge gas—fueled explosion deep underground ends hopes of rescuing the South Island coal miners, who were caught in a similar blast five days earlier.

2010- 33 miners are rescued after being trapped for 69 days in a gold and copper mine in Chile’s northern Atacama desert.

2010- 29 miners are killed in an explosion at West Virginia’s Upper Big Branch coal mine.

2007- At least 90 are killed in post—Soviet Ukraine’s worst mining disaster, after a methane blast rips through tunnels deep below ground in a coal mine near the eastern city of Donetsk.

2007- Six miners, three rescuers are killed in collapses at the Crandall Canyon coal mine in Emery County, Utah.

2006- 65 coal miners are killed from a gas explosion in San Juan de Sabinas, in northern Mexico’s Coahuila state.

2006- 12 killed in a methane explosion at the Sago coal mine in West Virginia.

2005- 214 miners die after an explosion deep in a coal shaft in southwestern China.

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