The organisation that controls the international diamond trade has failed to agree whether Zimbabwe should be allowed to resume diamond sales.
Following talks in Israel, members of the Kimberley Process said discussions had been "clouded" by the arrest in Zimbabwe of a human rights activist.
Farai Maguwu had alleged that forced labour was being used to develop Zimbabwe's new Marange diamond field.
Zimbabwe has accused the West of trying to hold back its economic development.
The diamonds from the Marange field could see the country become one of the world's top six exporters and generate $1.7bn a year.
But human rights groups want Zimbabwe to remain banned from selling "blood diamonds" - those which are used to fuel a conflict.
Despite extending their deliberations in Tel Aviv by a day, Kimberley Process chairman Boaz Hirsch announced on Thursday evening that they "could not reach consensus" regarding the work at Marange.
"As such, the meeting ended at an impasse," a statement said.
"This situation is unprecedented in the Kimberley Process meeting but all parties are committed to further engagement."
Further talks on whether to lift the worldwide ban on Zimbabwean diamonds would take place next month in the Russian city of St Petersburg, Mr Hirsch added.
The organisation angered human rights groups this month when a monitor it appointed to assess the mining operations at Marange said Zimbabwe had met the minimum conditions to resume exports.
On Tuesday, a Zimbabwean judge denied bail to Mr Maguwu after he was arrested for "peddling falsehoods" about the diamond trade.
The Kimberley Process suspended diamond exports from Zimbabwe last November in response to allegations of atrocities committed by security forces since 2008 against those who flocked to the Marange field when it was discovered.
Some 200 miners have allegedly been killed, while many have complained of harassment, torture and forced labour. Officials deny the allegations.
Zimbabwe's government said on Wednesday that it planned to sell diamond stockpiles from Marange regardless of the Kimberley Process decision.
The organisation was set up in 2002 after the diamond trade was accused of fuelling conflicts in Africa.