The ceremony was to be held in the In Ates region near Niger's capital Niamey, after the regional chief announced that all his slaves would be freed.
However, the chief backed out of the ceremony at the last minute, expressing fear that publicly freeing slaves would incriminate him under a March 2004 law banning slavery.
Romana Cacchioli of London-based Anti-Slavery International said that despite her initial concern at the cancellation, the fact the law had been acknowledged was a positive development.
"The interior minister has gone on national TV with a message from the ministry of interior saying that this [slavery] is a crime," she told Aljazeera.net
"We are pleased by the fact that for the first time they are saying they will pursue any acts of slavery," she said.
The ceremony was intended to mark the beginning of the enforcement of the slavery law in the African country and was to be attended by politicians and journalists.
Activists and development agencies have been pressuring Niger to ban slavery, a practice that has a history spanning centuries.
The president of an anti-slavery organisation in Niger told Aljazeera.net that the law was a step forward.
Niger is one of the poorest
countries in the world
"It's also a great thing that now a slave can lodge an official complaint that will be taken seriously," said Ilguilas Weila of the Timidria group.
The law outlawing slavery carries punitive measures of up to 30 years in prison.
According to Anti-Slavery International there are at least 43,000 slaves in Niger.
However, there is doubt over the government's commitment to the ban.
"The government is not serious about implementing the law, they are just interested in window-dressing - telling the world that there is no more slavery in Niger while covertly allowing this practice to continue," Weila told Aljazeera.net.
Niger is in need of assistance to
continue banning slavery
Niger is one of the poorest countries in the world and the government does not have the resources required to ensure the ban is upheld.
"We commend the government but it really is only the first step," Cacchioli said. "So we are calling on other development agencies to come to Niger's assistance. The government really does need help."
Cacchioli said she also hoped Western governments would provide assistance in the form of new livestock and education materials that would allow slaves to begin new lives when they were freed.
Slaves in Niger are made to work as domestic servants and farm workers without pay and for meagre food and shelter.
"These slaves live in abject poverty," said Cacchioli.
Slaves 'are basically treated no better than animals and often worse than animals'
"There are two grades of slaves, those who are domestic servants who are basically treated no better than animals and often worse than animals," she said.
For "those who are farm workers, their masters can often call on their slaves at any time to do unpaid labour … they are often living on the very edges of the Sahara so they do not have access to water."
Children born into slave families are often removed from their parents, sexual and physical abuse is common and slaves can be given or sold to other owners.
Slaves in Niger do not have the right to vote and their masters are still able to seize a slave's property and choose who he or she marries, even if the slave has not been in captivity for years.
The practice of slavery is also ongoing in other African countries such as Chad, Mali and Mauritania, Cacchioli said.