Negotiators have failed to reach agreement on a landmark treaty to curb plastic pollution, the diplomat chairing the talks has said.

Nearly 200 nations are taking part in a meeting in Busan, South Korea, which is intended to result in a landmark agreement after two years of discussions. A week of talks has failed to resolve deep divisions between “high-ambition” countries seeking a globally binding agreement to limit production and phase out harmful chemicals, and “like-minded” nations who want to focus on waste.

A draft text released on Sunday afternoon after multiple delays included a wide range of options, making clear the ongoing level of disagreement.

When an open plenary session finally convened late on Sunday night, the chair, Luis Vayas Valdivieso, said progress had been made but “we must also recognise that a few critical issues still prevent us from reaching a comprehensive agreement”.

He said: “These unresolved issues remain challenging and additional time will be needed to address them effectively. There is a general agreement to resume the current session at a later date to conclude our negotiations.”

His comments reflected earlier calls from delegates for a follow-up to the so-called INC5 talks, given the ongoing divisions.

“If you ask me … we stop, we adapt the paper as it is and we try to do another session,” Senegal’s Cheikh Sylla said. That would offer time “to bring the positions closer together, and at this session … we can reach an agreement that is balanced”.

Earlier, delegations seeking an ambitious treaty said a handful of countries were steadfastly blocking progress. A French minister accused the like-minded group of “continuing obstruction,” while a Rwandan delegate, Juliet Kabera, said a “small number” of countries “remain unsupportive of the measures necessary to drive real change”.

“Rwanda cannot accept a toothless treaty,” Kabera said.

While countries have declined to directly name those preventing a deal, public statements and submissions have shown that mostly oil-producing nations including Saudi Arabia and Russia have sought to block production cuts and other ambitious goals.

A Portuguese delegate, Maria João Teixeira, said earlier on Sunday that another round of talks might be the best option for a meaningful deal. “We are really trying to not have a weak treaty,” she said.

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Environmental groups had pushed ambitious countries to call a vote if progress stalls and said another round of negotiations was unnecessary. Eirik Lindebjerg, the global plastics policy lead at WWF, said: “We know what we need to do to end plastic pollution … simply adding more meetings is not the solution.”

More than 100 countries support setting a target for production cuts, and dozens also back phasing out some chemicals and unnecessary plastic products. Left unclear is the position of the world’s top two plastics producers, China and the US. Both were notably absent from the stage at a press conference on Sunday by countries urging a strong treaty.

“They are still considering and we are hopeful that there will be some interest on their part,” said Mexico’s head of delegation, Camila Zepeda. “This coalition of the willing is an open invitation. And so it’s not like it’s them against us.”

Panama’s Juan Carlos Monterrey Gómez told colleagues that “history will not forgive us” for leaving Busan without an ambitious treaty. “This is the time to step up or get out,” he said.