Indonesia has extended a landmark moratorium aimed at preserving the archipelago's vast swathes of tropical rainforest, but environmentalists said on Thursday the logging ban did not go far enough.

Large tracts of the country are covered in trees, including some of the world's most biodiverse rainforest that is home to endangered animals such as orangutans, tigers and elephants.

But huge swathes have been chopped down by palm oil, mining and timber companies in Southeast Asia's top economy, which has become the world's third-biggest carbon emitter as a result.

In 2011 Indonesia signed a two-year moratorium, which bans new logging permits for primary or virgin forest -- defined as forest not logged in recent history, as well as peatlands which store large quantities of carbon.

The scheme was created with help from Norway, which has pledged to pay out up to $1 billion to the government to preserve rainforests, depending on progress.

It protects an area of around 43 million hectares (106 million acres), according to environmental group the World Resources Institute.

The logging ban had already been extended once in 2013 to 2015, and President Joko Widodo on Wednesday signed a further two-year extension, telling reporters: "We need to protect our forests."

However environmental groups criticised the moratorium, saying that it still allowed deforestation for projects deemed in the national interest.

Infrastructure projects -- which Widodo is pushing in order to boost slowing economic growth -- and crop plantations are among those excluded from the ban.

"One of the biggest loopholes in the current policy is the clause that allows key strategic national priorities to be excluded," said Nirarta Samadhi, from the World Resources Institute.

Activists have also pressed the government to strengthen the moratorium to include other types of forest.

"Strengthening forests protection is urgent,” said Greenpeace Indonesia forests campaigner Teguh Surya. "President Joko Widodo has failed to listen to public demands to protect our remaining forests and peatlands."

The forestry minister said discussions were under way about strengthening the moratorium.