Indonesia's volcanology agency had warned since 2011 that it was unsafe to climb the country's active Marapi volcano, the organisation's chief said, days after the peak erupted and killed 13 climbers, with 10 still missing on Tuesday.

The 2,891-metre high volcano in West Sumatra erupted on Sunday, spewing gray clouds of ash as high as 3 kilometres (1.9 miles) into the sky.

Search operations for 12 missing climbers were under way on Tuesday, local authorities said, with about 200 local rescuers involved.

For more than a decade, Indonesia's volcanology agency had sent monthly letters warning the environment ministry and local conservation agency that climbers should keep a safe distance from the volcano's peak, said agency head Hendra Gunawan.

"The recommendation was to not climb up to the peak, that no one should go within 3 kilometres of the crater," he told Reuters.

Officials from the volcanology body said that it could only issue safety warnings, and that it was up to the environment ministry and local authorities to enforce them.

The environment ministry did not immediately respond to questions from Reuters.

The conservation agency, which is under the ministry, said permits to climb were given after getting the green light from several local agencies, including the West Sumatra provincial government and national disaster agency, as well the Padang search and rescue agency.

The search and rescue agency declined to comment. The national disaster agency did not immediately respond to a request for comment. West Sumatra's provincial government was not immediately reachable for comment.

Rescuers said there were 75 climbers on the volcano when it erupted.

Sunday's eruption of Mt. Marapi was the deadliest since 1979, when an eruption killed 60 people.

The volcano erupted several times in January and February 2023, but its relatively infrequent eruptions during the past decade have made it difficult to analyse, said Ahmad Basuki of the volcanology agency.

"Because we cannot record any seismic activity, the volcano gives no clear sign if it is going to erupt," he said. "The character of this volcano is dangerous."

Indonesia, which straddles the so-called "Ring of Fire", is home to more than 100 active volcanoes. (Reporting by Ananda Teresia, Writing by Kate Lamb, Editing by XXX)