Mohamed Nasheed, the first democratically elected president of the Maldives and a crusading advocate for climate action, resigned yesterday in what is being widely reported as a coup.

Environmental activists hailed Nasheed as a visionary and outspoken leader who put his tiny Indian Ocean archipelago on the map in the international climate change arena.

"President Nasheed may be the finest leader on climate the world has known," tweeted Bill McKibben, founding director of the climate action group 350.org.

Nasheed made a splash in 2009 when he donned scuba gear and held an underwater Cabinet meeting in an attempt to spotlight the threat of rising sea levels. He also pledged that the Maldives would go carbon-neutral by 2020, a plan that his climate change adviser Mark Lynas called "typically ambitious" yesterday.

Writing in The Guardian, Lynas called the overthrow of Nasheed "a blow to the Maldives and to democracy."

According to press reports, Nasheed's resignation came amid weeks of unrest and a policy mutiny. Nasheed handed power to Vice President Mohamed Waheed Hassan Manik, saying in a televised address, "I resign because I am not a person who wishes to rule with the use of power. ... I believe that if the government were to remain in power, it would require the use of force, which would harm many citizens."

It remained unclear late yesterday where Nasheed was being held. Reuters has reported that the military is holding him in protective custody on the orders of the opposition party.