MANAGUA (Reuters) - Tomas Borge, one of the founders of Nicaragua's leftist Sandinista movement who served as interior minister after the 1979 revolution that toppled U.S.-backed dictator Anastasio Somoza, died on Monday at the age of 81.

The former guerilla fighter, considered one of the hardliners in Daniel Ortega's government in the 1980s, was hospitalized earlier this month for a lung infection and was moved to intensive care after complications from surgery.

"It is with profound sorrow that we announce the end ... of the fruitful life of the revolutionary Tomas Borge," government spokeswoman Rosario Murillo, who is also the wife of Ortega, the current president, told local radio late on Monday.

Murillo did not disclose the cause of death.

Borge helped found the Sandinista National Liberation Front (FSLN) in 1961 and was jailed for plotting to overthrow the right-wing Somoza.

Borge was among the nine Sandinista leaders who first put Ortega in power after the revolution. He served as a powerful interior minister in Ortega's leftist government for most of the 1980s.

President Ronald Reagan saw the Sandinistas as a threat and backed the right-wing Contras in a decade-long civil war that killed around 30,000 people and wrecked the Central American nation's economy.

Ortega and the Sandinistas were voted out of power in 1990 but have since returned to power, winning a landslide reelection last November.

Borge, born on August 13, 1930, served as a congressman and ambassador to Peru and Ecuador, later moderating his more extreme leftist views and even backing free trade deals in the region with the United States.

He also wrote several books.

In the late 1990s he was drawn into a sexual abuse scandal that tarnished the reputation of top Sandinista leaders, when a female party member accused him forcibly of kissing and touching her when she worked as his interpreter.

(Reporting by Ivan Castro, writing by Mica Rosenberg; Editing by Paul Simao)