The world's biggest nature protection conference opens in Colombia Monday with the United Nations chief calling for countries to "convert words into action" and fatten a fund seeking to address biodiversity loss.

On the eve of the official start of the conference, UN Secretary-General Antonio Guterres urged "significant investment" in the Global Biodiversity Framework Fund (GBFF) created last year, as well as "commitments to mobilize other sources of public and private finance."

"Those profiting from nature must contribute to its protection and restoration," Guterres said in a video played to delegates gathered in the western city of Cali, where authorities were on high alert after threats from a guerrilla group.

The GBFF was created last year to help countries achieve the goals of the so-called Kunming-Montreal Global Biodiversity Framework (GBF) adopted in Canada in 2022 with 23 targets to "halt and reverse" the loss of nature by 2030.

So far, countries have made about $250 million in commitments to the fund, according to monitoring agencies.

The fund is part of a broader agreement made in Montreal two years ago for countries to mobilize at least $200 billion per year by 2030 for biodiversity, including $20 billion per year by 2025 from rich nations to help developing ones.

Guterres highlighted that destroying nature increases conflict, hunger and disease, fuels poverty and negatively impacts economic growth.

"A collapse in nature's services -- such as pollination, and clean water -- would see the global economy lose trillions of dollars a year, with the poorest hardest hit," he said.

'Peace with nature'

About 12,000 delegates from nearly 200 countries, including 140 government ministers and a dozen heads of state are expected at the 16th Conference of the Parties (COP16) to the UN Convention on Biological Diversity (CBD), running until November 1.

Themed "Peace with Nature," it has the urgent task of coming up with monitoring and funding mechanisms to ensure the 23 UN targets can be met.

But Colombia's EMC rebel group, a splinter of the FARC guerrilla army that disbanded in 2017, has cast a shadow over the event by urging foreign delegations to stay away and warning the conference "will fail."

The threat came after EMC fighters were targeted in a military raid in the southwest Cauca region, where the group is accused of engaging in drug trafficking and illegal mining.

Cali is the nearest large city to territory controlled by the EMC, which has been engaged in fraught peace negotiations with the government.

Colombian President Gustavo Petro also addressed Sunday's ceremonial event, two days after saying he was "nervous" about security.

Cali's mayor Alejandro Eder insisted, however, that the authorities had matters under control.

"We have been working since February to safeguard the city of Cali," he said. "We have more than 10,000 police officers, we also have detachments of the Colombian Armed Forces guarding the entire perimeter of the city."

'Nature not a resource'

The delegates have their work cut out for them, with just five years left to achieve the target of placing 30 percent of land and sea areas under protection by 2030.

World-renowned British primate expert Jane Goodall warned ahead of the summit there was little time to reverse the downward slide.

"The time for words and false promises is past if we want to save the planet," Goodall told AFP this week.

According to the International Union for Conservation of Nature (IUCN), which keeps a red list of threatened animals and plants, more than a quarter of assessed species -- about a million altogether -- are threatened with extinction.

Taking over the presidency of the COP, held every two years, Colombian Environment Minister Susana Muhamad told delegates that the goal of "peace with nature, implies a conceptual change in values.

"Nature is not a resource. Nature is the fiber of life that makes our own existence possible," she said.

Host Colombia is one of the most biodiverse countries in the world, and Petro, its first leftist president in modern history, has made environmental protection a priority.

But the country has struggled to extricate itself from six decades of armed conflict involving leftist guerrillas such as the EMC, right-wing paramilitaries, drug gangs, and the state.