Sandinista leader Daniel Ortega, a former Marxist revolutionary who fought a U.S.-backed insurgency in the 1980s, has won Nicaragua's presidential election, according to results released Tuesday.

With 91 percent of the vote counted, Ortega had 38 percent of the vote compared to 29 percent for Harvard-educated Eduardo Montealegre. Under Nicaraguan law, the winner must get 35 percent and have a 5 percentage point lead to win the election outright and avoid a runoff.

Montealegre immediately recognized the results, but said he and his party's lawmakers would spend the next five years ensuring that Ortega stayed true to his promises to support free trade and promote private business.

"We promise to continue our fight," he said.

Ortega was expected to speak later Tuesday. The former president spent most of the 1980s fighting a U.S.-backed Contra insurgency. He lost the presidency in the 1990 election, ending Sandinista rule and years of civil war, and has spent the past 16 years trying to get his old job back.

The United States, which warned against an Ortega win, has declined to comment on the results.

But former U.S. President Jimmy Carter, who served as an election observer, said Tuesday in Managua that U.S. Secretary of State Condoleezza Rice "assured me that no matter who was elected, the U.S. will respond positively and favorably." Rice's office confirmed that the two talked by phone, but refused to give details.

With the Cold War icon's victory, Nicaragua joined the list of Latin American nations with leftists at the helm. Leftist Venezuelan President Hugo Chavez, who has tried to help Ortega by shipping discounted oil to the poor, energy-starved nation.

"Latin America is ceasing to be — and forever — a backyard of U.S. imperialism. Yankee, go home!" Chavez said Tuesday in Venezuela.

Ortega's supporters celebrated in the streets, setting off fireworks.

Ortega, who served as president from 1985-90, toned down his once-fiery rhetoric during the campaign, promising to support a regional free trade agreement with the U.S. and maintain good relations with Washington.

He says he has changed profoundly since he befriended Soviet leaders, expropriated land and fought Contra rebels in a war that left 30,000 dead and the economy in shambles.