Paya was the lead organiser of the Varela Project, a signature-gathering drive regarded as the largest nonviolent campaign to change the system Fidel Castro established in 1959.
The government said he died in a car crash in Bayamo, Cuba, in July 2012 when the car he was riding in struck a tree, but his family insists the crash was not an accident and has pressed for an international investigation.
Power, a former foreign policy adviser to President Barack Obama, made her appeal, yesterday on her second day as US ambassador. She spoke with Cuban Foreign Minister Bruno Rodriguez at a lunch hosted by Argentine President Cristina Fernandez, who had just chaired a Security Council meeting.
The encounter was a rare meeting between a US ambassador and a Cuban foreign minister.
Cuba and the United States have not had diplomatic relations since the 1959 communist revolution that brought Fidel Castro to power, though both countries are represented at the United Nations.
In June, Paya's daughter Rosa Maria said she decided to seek refuge in Miami after facing continued repression on the island. Rosa Maria, 24, said she and her family had been the subject of threats, harassment and increased vigilance since her father's death.
