ISTANBUL/ANKARA - The death toll of Turkey's coal mine accident Tuesday has risen to 232 Wednesday as the country declares a three-day national mourning.

Prime Minister Recep Tayyip Erdogan has arrived at the site of the accident in the western province of Manisa, where hundreds of miners remained trapped underground.

Energy Minister Taner Yildiz said most of the victims died of carbon monoxide poisoning following a fire and explosion at the mine in the district of Soma.

The disaster occurred in the privately-owned mine during a shift changeover. The fire broke out 150 meters underground, Yildiz said.

He said the accident could become "the worst disaster" in Turkish history, since hundreds more remained trapped underground.

Turkish President Abdullah Gul has cancelled an official visit to China, scheduled for May 15-21, over the disaster. Prime Minister Recep Tayyip Erdogan has also called off a trip to Albania.

Yildiz, the energy minister, said that 363 miners of the 787 who were working underground at the time of accident have been accounted for, including the deceased.

Rescue efforts are continuing, but hopes of finding more survivors are diminishing.

The accident has sparked widespread anger as many denounced poor safety measures, accusing the government and mine companies of "negligence."

Anti-government protests were staged in Istanbul, Ankara, Izmir, Antalya and other cities over the latest mining accident, demanding the resignation of the ruling Justice and Development Party, AKP.

More than 500 people gathered in front of the Soma Holding headquarters in Istanbul around noon Wednesday.

In the capital Ankara, riot police fired tear gas and water cannon at hundreds of university student protesters who tried to march to the Ministry of Energy, daily Hurriyet reported.

The Worker Unions announced a nation-wide general strike on Thursday.

Also on Wednesday, a coal mine operating without a license collapsed in Gelik village of the Black Sea province of Zonguldak in northern Turkey, trapping the owner underground, according to private Dogan News Agency.

Mining accidents kill dozens of miners each year in Turkey.

The last major mining tragedy in Turkey occurred in 1992, when a fire and explosion killed 263 people. Two other mining accidents took place in 1983 and 1990, leaving 103 and 68 dead respectively.

In a related development, Iran's Foreign Ministry Spokeswoman Marzieh Afkham offered condolences to Turkey on Wednesday over the latest mining disaster and expressed readiness to help the rescue efforts, Tasnim news agency reported. (Xinhua)