Nicaraguan President Daniel Ortega, a former Marxist guerrilla leader, took a big early lead in Sunday's presidential election after heavy social spending won him strong support among the country's poor.

Nicaragua's electoral commission said preliminary results showed Ortega had secured 63.7 percent support based on a count of votes from 18 percent of polling stations.

His closest rival, radio personality and businessman Fabio Gadea, was way off the pace, back on 29 percent.

The lead was bigger than the win projected by opinion polls and Gadea supporters accused Ortega's Sandinista party of manipulating the electoral process, stuffing ballot boxes and making it hard for conservatives to cast their vote.

There were also outbreaks of violence during voting, with nine people injured in a clash in northern Nicaragua.

Ortega has overseen a period of economic progress in his five years in power, backed by financial aid from his socialist ally in Venezuela, President Hugo Chavez.

A former commander of the Sandinista rebel army that won power in a 1979 revolution and a Cold War adversary of the United States, Ortega has solidified his hold on Central America's poorest country with programs to improve health and education, microcredits and gifts of livestock.

There's no denying Ortega has done lots of good things, he's helped a lot of poor people, said Karla Flores, a 29-year-old mother of three from Masaya, southwest of the capital. He's got to keep up the good work.

Ortega's task has been made easier because his two main conservative opponents failed to join forces against him.

But he was only able to run for re-election thanks to a 2009 ruling by the Supreme Court -- which his Sandinista party controls -- that did away with a ban on consecutive terms.

Backed by Venezuela, Ortega has reduced poverty in this largely agrarian nation and is credited with allowing the private sector to operate freely.

Yet the court's decision has led to accusations that Ortega, who first served as president between 1985 and 1990, aims to stay in power indefinitely like Chavez.

How can Ortega call himself a revolutionary when he's a dictator? Roberto Betancourt, who has a farm on the outskirts of Managua, said at a polling station. He has no principles, he's following in the footsteps of Somoza.

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Since returning to office in 2007, Ortega has presented himself as a devout Christian, and swapped his military fatigues for white shirts and the red and black Sandinista flag for pink banners on the campaign trail.

His relations with Washington remain tense and the U.S. government said it was concerned about irregularities ahead of the election, including difficulties some voters had to register and some domestic observers to get accreditation.

Ortega has moderated his socialist rhetoric in recent years, although he is part of the Chavez-led bloc of left-wing governments in Latin America. Critics say he is too dependent on Venezuelan aid, but the funding has brought results.

Poverty has fallen to 57 percent of the population from 65.5 percent in 2005, according to government and World Bank statistics. Despite that, Nicaragua is still second only to Haiti as the poorest country in the Western Hemisphere.

(Additional reporting by Alex Leff and Sean Mattson; Editing by Kieran Murray and Vicki Allen)