It is alleged widespread human rights abuses took place in Marange
Zimbabwe President Robert Mugabe has threatened to quit the Kimberley Process (KP) - the body which ensures diamonds do not fund conflicts.
"We can sell our diamonds our own way," Mr Mugabe said as he opened a trade and tourism fare in Harare.
The president and his allies have been accused of rights abuses in the eastern Marange diamond field.
The KP gave Zimbabwe until June to prove the Marange field was being properly run.
However, last month Zimbabwe cancelled a diamond sale after officials failed to get KP approval for the gems.
"We are trying to play their way, but we could go outside that KP system and do it otherwise," said Mr Mugabe.
Analysts say the only way open to Zimbabwe would be the black market.
Activists have long accused the military of carrying out widespread atrocities in the Marange fields.
They say there is evidence of mass evictions, forced labour and murders by security forces.
They also claim that the profits from the stones go to Mr Mugabe and his allies, who joined a unity government a year ago.
They have always denied the allegations.
Late last year, rights activists pressured the KP group to suspend Zimbabwe's membership.
But the group instead opted for a June deadline for the Marange fields to be cleaned up - a decision criticised as too lenient by rights groups.
Meanwhile, the president dismissed the European Union's decision on Tuesday to extend sanctions against Mr Mugabe and his inner circle for another year.
It said the coalition government had not made enough progress, but Mr Mugabe said the extension was more proof that the EU did not want poorer nations to develop.