The assembly has been working on a new draft constitution that will go to a referendum on Sept. 4, and eliminating or reforming the senate has been a key goal of left-wing members, who say it stalls or halts progress and laws.

Opponents said the proposal would give too much power to the lower house and centralize decision-making.

"Regions wouldn't have a voice when it comes to health, pensions, transport or education," Hernan Larrain, a conservative constituent said on the assembly floor.

While the article creating the new body reached the two-thirds majority needed to be included in the constitution, the article defining its powers failed and will now go back to the commission for further debate and another vote.

Ricardo Montero, a constituent and coordinator of the commission, told reporters that the commission will rework the agreement to garner more support. "Without a doubt we're worried about some of the articles that failed," he said.

Eliminating the senate had divided the commission earlier in negotiations and led to a medley of conflicting proposals largely voted down by the full assembly last month.

The new agreement came after polls showed support for the new constitution faltering, with some voters saying infighting and extreme proposals were causing them to lose faith in the process.

The assembly has until May 17 to approve articles before handing over the draft constitution to a commission in charge of fine-tuning the document.

"This is a very complex topic, very technical," Rosa Catrileo, a constituent and commission coordinator told reporters after the vote. "It's a challenge, we have little time, but we still have time."

Next week the constitutional assembly is set to vote on articles that could redefine water rights and reshape mining rights in the world's no. 1 copper producer.