* Death comes on 24th anniversary of coup against Stroessner
* Rescuers find Oviedo's charred body in helicopter crash
* Government declares three days of mourning
* He had been campaigning in northern province of Concepcion (Adds details, byline, color throughout)
By Daniela Desantis and Mariel Cristaldo
ASUNCION, Feb 3 (Reuters) - Paraguayan presidential candidate Lino Oviedo, who helped the lead the 1989 coup that overthrew dictator Alfredo Stroessner, died in a helicopter crash over the weekend.
A retired general known as a dynamic public speaker, the 69-year-old Oviedo was running in the April presidential election in the impoverished and politically unstable South American country.
Police rescuers found his body on Sunday in the wreckage of a helicopter crash in northern Paraguay where he was traveling for a campaign event. The day, Feb. 3, marked exactly 24 years since the coup that ended Stroessner's 35-year dictatorship.
"On behalf of the government, we send our sincere condolences to the family of General Lino Cesar Oviedo," Paraguayan President Federico Franco said in a Tweet.
The government decreed three days of mourning and suspended all official activities.
Oviedo was accused of plotting to overthrow governments in the 1990s and sentenced to 10 years in jail. He was pardoned before completing the term and returned to politics as leader of the conservative National Union of Ethical Citizens party.
"He is a person who unquestionably figures in the history of our country, with all its light and shadows," Paraguay's Communications Minister Gustavo Kohn said.
The latest photos on Oviedo's Facebook page show him wearing a straw hat and plaid shirt, speaking on Saturday at a political rally in the northern province of Concepcion.
Interior Minister Carmelo Caballero said the government would investigate the crash, which occurred on Saturday night as Oviedo was flying back to capital Asuncion in adverse weather.
"We cannot rule out any hypothesis," Caballero said.
Paraguay's previous president, Fernando Lugo, was removed from power by Congress in June when lawmakers voted to remove him for failing to keep the peace after 17 police and peasant farmers died in clashes over a land eviction. The leftist leader was a year from completing a five-year term.
Lawyers for former Roman Catholic bishop Lugo questioned the constitutionality of his lightning-quick impeachment. But the country's top electoral court ratified its legitimacy. (Reporting By Daniela Desantis and Mariel Cristaldo, Writing by Hugh Bronstein; Editing by Sandra Maler)