Ten people were arrested after a series of raids across Portugal on Monday as part of the investigation.
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Portugal has carried out a series of raids as part of an investigation into diamond smuggling involving suspect United Nations troops.
Portuguese soldiers are suspected of trafficking diamonds, drugs, and gold back into Europe.from the Central African Republic.
Police said they had carried out a major crackdown on a criminal network that used the soldiers as "couriers" to transport the items on military aircraft.
Ten people were arrested after raids at around 100 locations across Portugal, they added in a statement.
The investigation was focused on "a criminal network with international connections that derived illicit income from diamond smuggling and drug trafficking".
"What is at issue at the moment is the possibility that some of the soldiers who took part in the National Force detached to the CAR were used as couriers in the trafficking of diamonds, gold, and narcotics".
Authorities were first alerted in December 2019 by the command of a detached force, the police and armed forces added.
Portuguese Defence Minister João Gomes Cravinho told the Lusa news agency that the situation was "deeply regrettable".
Cravinho said that Portugal's government had informed the UN of the investigation last year.
"An investigation is underway to determine what happened and to take the exemplary measures that need to be taken," added Portuguese President Marcelo Rebelo de Sousa.
Hundreds of elite Portuguese troops, including paratroopers and commandos, have been stationed with the UN force in the Central African Republic in recent years.