HONG KONG - Environmental activists hailed on Tuesday Indonesia's ban on converting peatlands into plantations but said enforcement was critical to reducing annual fires that shroud parts of Southeast Asia in choking haze.

Indonesia announced on Monday that companies were banned from turning peatlands into palm oil and other types of plantations, and must restore peatlands they have degraded.

Peat soils contain huge quantities of carbon in the form of organic matter, which accumulates over hundreds of years and provides nutrients for plant growth.

When peatlands are drained or cleared by fire to make way for plantations, the carbon is released into the atmosphere.

Environmental experts welcomed Indonesia's ban in light of a global accord signed in Paris last year to lower carbon emissions blamed for a warming planet.

"This regulation will be a major contribution to the Paris climate agreement and a relief to millions of Indonesians who suffer the effects of toxic haze from peat fires," said Nirarta Samadhi, Indonesia country director for the World Resources Institute thinktank, in a statement.

Indonesia, the world's 6th largest emitter of greenhouse gases, according to the country's Peatlands Restoration Agency, has more than 15 million hectares of peatlands, an area twice the size of Ireland.

WRI estimates by 2030, the new ban could help Indonesia cut up to 7.8 gigatons of carbon dioxide emissions, equivalent to roughly all the annual greenhouse gases emitted by the United States.

Peaty soil, found in many parts of Indonesia, is particularly flammable when dry, often causing fires to spread beyond their intended areas.

Every year smoke from fires used to clear land for palm oil and pulp and paper plantations in Indonesia clouds the skies over much of the region, raising concerns about public health.

Indonesia has been criticized by neighbors and green groups for failing to end the annual fires, which were estimated to cost Southeast Asia's largest economy $16 billion in 2015, and left more than 500,000 Indonesians suffering from respiratory ailments.

Yuyun Indradi, a forest policy researcher at the Jakarta office of international campaign group Greenpeace, said Indonesia's ban was a "good move."

However, Indradi said Indonesia had introduced several moratoria aimed at protecting the environment before.

"A key problem has been enforcement and lack of transparency," Indradi told the Thomson Reuters Foundation, adding that previous environmental policies - such as requiring companies to protect carbon-rich deep peatlands - had been widely ignored.

"The big question will be how to get the new regulation enforced," he said.