The violence in Guinea could worsen and spill over into a bloody civil war, an international think tank has warned.
The 18-hour curfew has been imposed to stop further protests
The International Crisis Group (ICG) criticised President Lansana Conte for declaring martial law and imposing an 18-hour curfew to curb demonstrations.
The African Union (AU) also called for an end to the "ominous situation involving the killing of citizens".
Union leaders and the government have held their first talks since martial law was announced earlier this week.
After a brief meeting, discussions are now set to resume on Saturday.
Religious, business and military leaders also took part in the talks, initiated by speaker of parliament Aboubacar Sompare, reports the AFP news agency.
But the BBC's Wills Ross in the capital, Conakry, says not all union leaders were there.
Arriving at Guinea's parliament, one union leader, Serah Rabiatou Diallo, expressed hope that the negotiations with the military would produce a solution to end the political crisis.
She said the immediate priority was the lifting of the state of siege, which is effectively martial law.
The ICG estimates that more than 100 people have died since the general strikes and protests started in January.
"If the Conte regime continues to rely on military repression, it could rapidly bring Guinea to a dramatic spiral of violence: full popular insurgency, with increasing chaos that is likely to stimulate a bloody, military take-over," the ICG said in a statement.
This could lead "to a possible civil war comparable to those that have torn apart its neighbours in the past decade with uncontrollable consequences".
Guinea borders Sierra Leone and Liberia, which are both emerging from a decade of conflict.
Both the ICG and AU called for negotiations to end the crisis in Guinea.
"We call up upon the president and government of Guinea to use all peaceful means to restore normalcy to the country," Ghana's President John Kufuor, who is currently head of the AU, said at the Franco-African summit in the French resort of Cannes.
Correspondents say the violence has reduced since the introduction of martial law, but there is a great deal of uncertainty.
Many businesses have shut and even residents organising funerals have had to apply to neighbourhood officials for permission to come together in a large group, AP news agency reports.
Residents in different suburbs of the capital, Conakry, say that they often hear shooting.
The army has been given wide powers
"They started shooting again this morning. It's been two days that we haven't gone out and haven't slept," Aminata Cisse told AP.
Human rights groups complain that having been given widespread powers, many civilians had been subjected to harassment by soldiers.
Outside the capital, the UN's World Food Programme says that several of its warehouse have been looted.
An estimated $350,000 worth of food was looted from three warehouse over the weekend.
A fourth warehouse was looted on Tuesday morning in the northern town of Labe, AFP reports.
Last month, the unions called off their 18-day strike after Mr Conte promised to hand over powers to a prime minister.
But they renewed the strike action call after saying the man named last Friday for the post, Eugene Camara, was too close to Mr Conte.
The unions want Mr Conte to step down, saying he has mismanaged the economy.
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