The fifth United Nations Intergovernmental Negotiating Committee meeting to yield a legally binding global treaty in Busan, South Korea, was meant to be the final one.
However, countries remained far apart on the basic scope of a treaty and could agree only to postpone key decisions to a future meeting.
"While I saw points of convergence in many areas, positions remain divergent in some others," said Luis Vayas Valdivieso, the chair of the meeting.
The most divisive issues included capping plastic production, managing plastic products and chemicals of concern as well as financing to help developing countries implement the treaty.
The idea of capping plastic production has not been approved by delegates at talks in South Korea. (AP PHOTO)
An option proposed by Panama, backed by more than 100 countries, would have created a path for a global plastic production reduction target while another proposal did not include production caps.
The fault lines were apparent in a revised document released on Sunday by Valdivieso, which could have formed the basis of a treaty, but remained riddled with options on the most sensitive issues.
"A treaty that ... only relies on voluntary measures would not be acceptable," said Juliet Kabera, director general of Rwanda's Environment Management Authority.
"It is time we take it seriously and negotiate a treaty that is fit for purpose and not built to fail."
A small number of petrochemical-producing countries, such as Saudi Arabia, have strongly opposed efforts to reduce plastic production and have tried to use procedural tactics to delay negotiations.
"There was never any consensus," Saudi Arabian delegate Abdulrahman Al Gwaiz said.
"There are a couple of articles that somehow seem to make it (into the document) despite our continued insistence that they are not within the scope."
China, the United States, India, South Korea and Saudi Arabia were the top five primary polymer producing countries in 2023, according to data provider Eunomia.
Had such divisions been overcome, the treaty would have been one of the most significant deals relating to environmental protection since the 2015 Paris Agreement.
The postponement comes just days after the turbulent conclusion of the COP29 summit in Baku, Azerbaijan.
At Baku, countries set a new global target for mobilising $US300 billion ($A460 billion) annually in climate finance, a deal deemed insufficient by small island states and many developing countries.
The climate talks were also slowed down by procedural manoeuvres by Saudi Arabia- who objected to the inclusion of language that reaffirmed a previous commitment to transition away from fossil fuels.
Some negotiators said a few countries held the proceedings hostage, avoiding compromises needed by using the UN's consensus process.
Senegal's delegate Cheikh Ndiaye Sylla called it "a big mistake" to exclude voting during the entire negotiations, an agreement made last year during the second round of talks in Paris.
Plastic production is on track to triple by 2050 and microplastics have been found in air, fresh produce and even human breast milk.
Chemicals of concern in plastics include more than 3200 found according to a 2023 UN Environment Programme report, which said women and children were particularly susceptible to their toxicity.
Despite the postponement, several negotiators expressed urgency to get back to talks.
"Every day of delay is a day against humanity. Postponing negotiations does not postpone the crisis," Panama's delegation head Juan Carlos Monterrey Gomez said on Sunday.
"When we reconvene, the stakes will be higher."
