At least 51 workers were killed in a coal mine explosion in northeastern Iran, according to local media on Sunday.

The explosion was caused by a rapid release of methane and carbon monoxide Saturday night in two blocks in the mine in Tabas in Khorasan province, the IRNA state news agency reported.

Local authorities said that about 70 workers were at the mine at the time of the explosion.

The explosions occurred in blocks B and C of the mine, managed by a private company, at a depth of about 200 meters (about 656 feet).

Iranian authorities cited difficulties in carrying out a rapid rescue operation due to underground conditions.

Iranian President Masoud Pezeshkian, who embarked on an official visit to New York on Sunday morning, had earlier ordered an investigation into the incident.

Minister of Industry, Mines, and Trade Mohammad Atabak, along with a team from the ministry, visited the site to oversee rescue efforts and initiate preliminary investigations.

He stated that the private company overseeing the mining operations in Tabas is under investigation, adding that a committee will be formed to investigate the cause and ensure future mine safety.

Iran's judiciary chief, Mohseni Ejei, has also instructed the provincial judiciary head in South Khorasan to conduct a swift investigation into "various aspects" of the incident and to take "appropriate legal action" against those found responsible.

Vice President Mohammad Reza Aref expressed his condolences to the victims' families and vowed to hold those involved in negligence or wrongdoing accountable.

Meanwhile, the provincial government in South Khorasan has declared three days of mourning, starting Monday, in the aftermath of the deadly incident, with top authorities extending their condolences.

The mine explosion and the accountability of those responsible are also on the parliament’s agenda, as speaker Mohammad Bagher Ghalibaf told local media.

He called the repeated occurrence of such incidents "regrettable."

In 2017, dozens of miners were killed in a large explosion at a coal mine in northern Iran's Golestan province. Similar incidents occurred in 2013 and 2009 in various provinces.

Iran is one of the world’s largest mineral producers, with thousands of iron, copper, gold, lead, and coal mines spread across the country, contributing significantly to its gross domestic product.