The world's next global pact for nature is doomed without clear mechanisms for implementing targets, conservation groups said Saturday on the sidelines of UN talks, as hundreds of protesters took to the streets of Montreal demanding greater action.

Similar factors were widely blamed for the failure of the last 10-year biodiversity deal, adopted in 2010 in Aichi, Japan, which was unable to achieve nearly any of its objectives.

"Strong text that commits countries to review progress against global targets and ratchet up action over time is essential to hold governments accountable," said Guido Broekhoven of the World Wide Fund for Nature (WWF), adding he was "very worried" about the current state of negotiations on this point.

Implementation mechanisms are at the heart of the Paris agreement on the fight against global warming, in the form of "nationally determined contributions."

However, the current text on biodiversity only "urges" countries to take into account the conclusions of a global review in four years' time -- without committing them to enhance action if the review finds targets aren't on track.

"So what we have on the table is barely an encouragement to maybe do better," Aleksandar Rankovic, of the US nonprofit Avaaz, told AFP.

"And there is no compliance mechanism being discussed that could help organize this necessary conversation between governments, on how they could cooperate better."

The UN meeting, called COP15, running from December 7 - 19, bringing together nearly 5,000 delegates from 193 countries to try to finalize "a pact of peace with nature," with key goals to preserve Earth's forests, oceans and species.

On a freezing Saturday, people young and old, including a large contingent of Indigenous Canadians, braved the biting cold to make their voices heard in Canada's second city.

Some wore costumes, dressed as birds, trees, and even caribou -- an emblem of Canada's boreal forests that are now threatened.

"The people are trying to speak, trying to say you can't just talk, you have got to act," said Sheila Laursen, part of the group Raging Grannies.

"Let's not forget that... to protect biodiversity we need to protect Indigenous people first, Indigenous people are protecting biodiversity," Helena Gualinga, who belongs to a tribe in the Ecuadoran Amazon.