LIMA, Peru - Left-wing former army commander Ollanta Humala claimed victory in Peru's presidential election on Sunday and tried to strike a conciliatory tone as investors and the opposition worry he will ruin a long economic boom.

With 84 percent of ballot boxes counted, Humala had a narrow but growing lead of 1.8 percentage points over right-wing lawmaker Keiko Fujimori, the daughter of jailed former president Alberto Fujimori.

Exit polls and quick counts showed Humala clearly ahead and his advantage in the official returns was expected to grow as more votes came in from poor, rural areas.

"We want to install a government of national unity," Humala, 48, told thousands of cheering supporters after a bruising race that brought back bitter memories of Peru's chaotic past.

One of the world's fastest-growing economies over the last decade, Peru is a major metals exporter, but a third of its citizens are stuck in poverty and Humala campaigned on promises to spread the country's wealth.

"We want economic growth with social inclusion," he said at a rally in downtown Lima that stretched into the early hours of Monday. "We can build a more just Peru for everybody."

Some danced in jubilation, others chanted "Humala Presidente!" and "Fujimori never again".

Humala narrowly lost the last presidential election in 2006 and has since toned down his more radical anti-capitalist policies to try to win over centrist voters.

But investors still worry he would increase state control over the economy and throw away fiscal discipline. Peru's stock market and its sol currency have stumbled on his rise in the polls and were expected to tumble later.