Guineans have been mourning those who died in the protest
US Secretary of State Hillary Clinton has labelled Guinea's crackdown on an opposition rally last Monday as a "vile violation" of people's rights.
Mrs Clinton promised "appropriate actions" against the military rulers.
Activists say soldiers killed 157 anti-junta protesters - though the government puts the figure much lower.
Opposition leaders have rejected the latest offer of talks with the junta - saying the perpetrators of the killings needed to be punished first.
They also said junta leader Captain Moussa Dadis Camara would have to step down before any talks could go ahead.
"We will only sit on the same negotiating table with the junta when these demands are met," said Ba Oury, a senior figure within the opposition.
Burkina Faso's President Blaise Compaore is mediating in the dispute and proposed the talks after holding meetings with both sides on Monday.
Guineans and governments around the world were horrified by eyewitness reports of soldiers firing on crowds and raping women in the streets as they put down the rally.
Mrs Clinton is the latest international leader to join a chorus of outrage over the crackdown in the capital, Conakry, on 28 September.
"The indiscriminate killing and raping that took place under government control by government troops was a vile violation of the rights of the people of that country," she said.
She pledged that the US intends "to pursue appropriate actions against the current administration in that country".
The rally was called to protest at reports that Captain Camara was planning to stand in presidential elections next year.
After seizing power in December 2008, he pledged not to contest elections but has since made a series of contradictory statements about his intentions.
He has even described himself as a "hostage" - both to the Guinean people and to the "unstructured" army.