Guinea's junta-appointed government has dissolved the country's leading opposition movement, the National Front for the Defence of the Constitution (FNDC), under a decree dated Saturday.

An alliance of political parties, trade unions and civil groups, the FNDC spearheaded protests against former president Alpha Conde before his ouster in a coup last year.

Friction has been growing for months between the FNDC and the junta, culminating in an announcement by the coalition on Monday that it would stage demonstrations on August 17.

A decree declaring the FNDC's dissolution, signed by Territorial Administration Minister Mory Conde, was authenticated by AFP on Tuesday.

"The de-facto group called the National Front for the Defence of the Constitution, is dissolved... with effect from the date of signature," the ruling said.

Rumours of the decree had spread on social media late Monday.

The decree said the FNDC's "operational mode is based on violent attacks (perpetrated) during banned demonstrations, attacks against individuals who do not share their ideology, and targeted attacks against the security forces".

The organisation has "the behaviour of combat groups and private militias... threatening national unity, public peace and cohabitation", it said.

Rich in minerals but deeply poor, the West African state has had little stability since it gained independence from France in 1958.

In 2010, Conde, today aged 84, became the country's first democratically elected president.

But his popularity dived in his second term as critics accused him of authoritarianism, and opposition protests were violently repressed.

Dozens died, the overwhelming majority of them civilians, in protests launched by the FNDC.

On September 5, as anger mounted over Conde's successful bid for a third term -- a move he defended on the grounds of a change to the constitution -- mutinous troops rebelled.

Junta strongman Mamady Doumbouya has pledged to return power to elected civilians within three years.

The timeline has put the junta into conflict with the region's bloc, the Economic Community of West African States (ECOWAS).

ECOWAS' chair, Guinea-Bissau President Umaro Sissoco Embalo, said late last month that he had convinced the junta to shorten the transition to two years. But the figure has not been confirmed by Guinea.

Demonstrations broke out in Guinea on July 28 and 29 over perceptions that the junta was dragging its feet on restoring civilian rule, leaving five dead.

The FNDC on Monday called for nationwide protests on August 17 to condemn the lack of "credible dialogue" and use of lethal weapons against demonstrators. The organisation is also calling for the release of jailed supporters.

The coalition's communications officer, Abdoulaye Oumou Sow, refused to comment Tuesday on the dissolution order.

But the Guinean Organisation for the Defence of Human Rights (OGDH) separately warned that "confiscating civil liberties or silencing all dissenting voices will only make the situation more complicated."

It said it was "very concerned... by the turn of events".

Two FNDC leaders, Oumar Sylla and Ibrahima Diallo, were jailed after the July demonstrations.

They have been charged with taking part in an illegal gathering, destruction of property and bodily harm.

The organisation suspended its activities for a week, including a demonstration planned for August 4, in response to an appeal for calm issued by ECOWAS on August 1.