(This November 28 story corrects paragraph 5 to show girlfriend spoke to Maldonado before arrest, not while in jail)

By Nicole Martinez

MIAMI (Reuters) - Cuban police have detained dissident artist Danilo "El Sexto" Maldonado, once declared a prisoner of conscience by Amnesty International, after he made a video celebrating the death of Fidel Castro, a dissident human rights group and the artist's girlfriend said on Monday.

Castro died on Friday at age 90, a decade after he had retired due to poor health and ceded power to his brother, current President Raul Castro.

Maldonado posted a video on social media on Saturday in which he rants against Castro and calls him a "mare," a Cuban pejorative.

Such a video could constitute the offense of "disrespect." Maldonado, 33, was previously jailed on that charge for painting the names "Fidel" and "Raul" on a pair of pigs.

His most recent detention was reported by Maldonado's American girlfriend, Alexandra Martinez, who said she spoke with him moments before he was detained by Cuban officials, and by the dissident Cuban Commission of Human Rights and National Reconciliation, which said Maldonado's mother reported the detention on South Florida radio.

Cuban officials have not confirmed whether Maldonado was in custody, said Kimberley Motley, a human rights attorney contacted by the Human Rights Foundation to handle Maldanado's case. Cuba does not publicly report arrests and dismisses dissidents as U.S.-paid mercenaries.

Maldonado has used performance and graffiti art to criticize the Cuban government.

Following his arrest in December 2014, he spent 10 months in prison and was released after an Amnesty International statement that he was considered Cuba's only prisoner of conscience.

(Reporting by Nicole Martinez; Editing by Daniel Trotta and Marguerita Choy)