An opposition rally two weeks ago ended in deadly violence
Guinea is in danger of slipping into dictatorship, the leader of West Africa's economic group, Ecowas, says.
Mohamed Ibn Chambas said the junta, who seized power late last year, was repressing the people with "arbitrary and irresponsible" use of state power.
Ecowas ministers are meeting in Nigeria to try to resolve the crisis in Guinea, sparked when soldiers opened fire on an opposition rally two weeks ago.
Guineans are holding a two-day strike to remember dozens who were killed.
Activists say 157 people were killed by troops, and rights groups have reported that soldiers raped women in the streets.
The government put the number of dead at 57 and said most had died in a stampede.
The AP news agency reports that Agriculture Minister Abdourahmane Sano has resigned in protest over the killings.
The country's military rulers were widely criticised over the shootings - with the US denouncing "vile abuses" perpetrated against their own people.
Critics of the military are hoping that the strike, combined with the Ecowas talks, will increase pressure on junta leader Captain Moussa Dadis Camara to resign.
Ecowas is hosting talks in Abuja where opposition leaders, members of Guinea's military and Ecowas foreign ministers met to try to resolve the crisis.
Opening the meeting, Mr Chambas told delegates Guinea was "characterised by arbitrary and irresponsible use of state power by the military to repress the population".
"The signs are there now that if the military junta has its way it will impose yet another dictatorship on them," the AFP news agency quoted him as saying.
Analysts say it is unusual for Ecowas to use such strident language.
The bloc suspended Guinea after last December's coup, when the military took power shortly after the death of long-term leader Lansana Conte.
The protests two weeks ago were sparked by persistent rumours that Capt Camara intends to stand for president in an election scheduled for next January - something he had previously ruled out.