Congo's government has criticised a decision to remove it from a list of countries recognised to be dealing legitimately in diamonds.
Congo could not explain where its diamonds came from
Mines Minister Philippe Mvouo said the decision by the watchdog Kimberley Process Certification Scheme was deplorable.
The action was prompted by accusations that it was smuggling gems on to the world market.
Saturday's suspension means Congo cannot trade with other member states.
Kimberley Process officials said Congo had been unable to explain the origin of the number of rough diamonds it exported.
Investigators concluded that it had been smuggling diamonds from other African countries and sending them through Switzerland and the United Arab Emirates to avoid detection.
Congo's neighbour, the Democratic Republic of Congo, has long accused Congo of smuggling diamonds from its territory.
But in a statement to the AFP news agency Mr Mvouo said the president of the Kimberley Process, which is based in Canada, had not respected the organisation's rules concerning the right to respond to allegations, mediation, and confidentiality.
"Kimberley Process participants need to have complete confidence that conflict diamonds are not entering the legitimate trade," said Tim Martin, the organisation's chairman.
"The removal of the Republic of Congo from the list of participants is necessary to safeguard the credibility and integrity of the KPCS."
Mr Martin said Congo would be allowed to rejoin the process "when it is in a position to fully implement the requirements of the certification scheme".
But Congo denies the allegations.
"The Republic of Congo affirms that she is able to take up her responsibilities under the Kimberly Process and is ready to contribute with neighbouring countries to curb the problematic circulation of rough diamonds," Mr Mvouo said.
Exclusion means Congo cannot trade diamonds with the process' 43 member states, which account for over 98% of the world's diamond trade.