After lengthy negotiations and record deaths of defenders on the continent, sources say a deal is very likely to be reached.

Ka’apor forest guardians patrolling the borders of their territory, in Maranhao state, Brazilian Amazon.

Ka’apor forest guardians patrolling the borders of their territory, in Maranhao state, Brazilian Amazon. Photograph: Lunae Parracho for the Guardian

Latin American countries are poised to agree the world’s first legally binding convention to protect environmental defenders at a conference in Costa Rica.

Land activists and indigenous people were killed in record numbers on the continent last year, with more than two nature protectors murdered every week.

Now, after two years of negotiations, UN and diplomatic sources say it is very likely that an environmental democracy treaty offering them legal protection will be agreed at the summit which ends on 4 March.

Constance Nalegach, Chile’s lead negotiator at the UN’s Economic commission for Latin America and the Caribbean (Eclac) meeting, said that a legal pact was now “the most probable result and [also] a political gain”.

“A legally binding instrument is the most useful agreement to ensure human rights,” she told the Guardian. “Even though it is not the whole solution, it is an important step for stopping and reducing socioenvironmental conflicts in the region, including the attacks on environmental defenders.”

Several countries are expected to sign the convention, but it will not enter into force until it has been formally ratified by eight of the commission’s member states.

Enforcement will take place at the national level, with a commission review mechanism monitoring states’ progress towards human rights norms.

Carole Excell, a director at the World Resource Institute, said the agreement in Costa Rica would be “a massive step forward”.

“It will start a snowball process and create huge momentum for an issue that countries weren’t even acknowledging as a problem until very recently,” she said.

Around the world, 197 land activists, indigenous people and wildlife rangers were killed in 2017, an estimated 60% of them in South America.

Mining, agricultural concessions and infrastructure projects took a heavy toll on nature protectors with paramilitaries often acting with impunity on behalf of vested interests in remote areas.

Treaty negotiations began in 2016 and were always intended to come up with a legal text of the sort now agreed and backed, UN officials say, by most countries.

“Therefore, it is highly likely that the meeting will finish with the adoption of the first ever legally binding agreement,” one UN source said.

The treaty would oblige signatories to take “adequate and effective measures” to protect and promote the rights of environmental defenders to life, and to free movement, expression, and assembly.

States would also be impelled to take “appropriate, timely and effective” measures to prevent threats or attacks against environmental defenders – and to investigate and punish them after they have occurred.

Some regional actors have been accused of complicity in the murder of environmental activists such as the Goldman award-winning campaigner Berta Cáceres who was killed in 2015.

Even so, diplomats told the Guardian that “at least two countries” were still opposing a legally binding pact. One of them, Mexico, has staked out a position for a weaker declaratory statement on environmental justice that diplomats say would not create “the necessary peer pressure” for strong enforcement.

Colombia and Brazil – the world’s two deadliest countries for environmental protectors – have also kept their final voting cards close to their chests.