Elizardo Sanchez said two plainclothes officials stopped him near his Havana home on Tuesday, shouting physical threats and using crude language. That night, dissident Guillermo Farinas was allegedly attacked by a man with a wooden stick elsewhere in Havana, resulting in light injuries.
There was no immediate comment from the Cuban government, which considers all of the dissidents to be mercenaries paid by Washington to stir up trouble.
The 68-year-old Sanchez runs the Cuban Commission for Human Rights and National Reconciliation and acts as a de facto spokesman for the island's small opposition group. He made the accusations in a letter sent to foreign journalists Thursday that included an official complaint he lodged with Cuban Interior Minister Abeladro Colome the previous day.
"Arbitrary arrests, physical aggression, threats and humiliations against peaceful citizens are counterproductive to the necessary alternative that is a national dialogue," Sanchez wrote in the letter to Colome.
Cuban President Raul Castro freed dozens of opposition activists and social commentators in 2010 following a deal ironed out with the Roman Catholic church. But dissidents continue to complain about increasingly frequent incidents of harassment
The opposition has accused the government of a wave of intimidation in recent weeks, including the 19-day detention of Antonio Rodiles, an activist in Havana who heads a project called State of Sats, which organizes debates about Internet access and other social issues.
Supporters say Rodiles was roughed up during his arrest. He was freed on Wednesday.
Follow Paul Haven on Twitter: http://www.twitter.com/paulhaven.