Factbox: Candidates in Colombia's presidential election

(Reuters) - President Juan Manuel Santos and opposition challenger Oscar Ivan Zuluaga are in a tight race ahead of a second-round vote on June 15 for Colombia's top job, in an election campaign being held against a backdrop of peace talks with Marxist rebels. Here are the two candidates and their policies. JUAN MANUEL SANTOS As defense minister for former President Alvaro Uribe, Santos led a successful campaign against the Revolutionary Armed Forces of Colombia (FARC) rebels. Uribe and Santos were allies, but after his 2010 election victory, Santos broke with Uribe and later opened peace talks with FARC. He won support with promises to end the war and help the economy, but the slow pace of the talks has made many impatient and spurred criticism that he is offering too many concessions. A U.S.-trained economist, Santos warns the talks could collapse if he is not re-elected. He has received the backing of leftist candidate Clara Lopez, a peace talks supporter who won 15.2 percent of the vote in the first round. Born into one of Colombia's most powerful families, the president, 62, has followed market-friendly economic policies, helping to sustain solid growth. OSCAR IVAN ZULUAGA Zuluaga surged in the polls on promises to defeat the rebels on the battlefield, a strategy championed by his mentor, Uribe, as well as by vowing to improve education and healthcare. The 55-year-old Zuluaga, who served as finance minister under the former president, says the government should not negotiate with the FARC while they are still at arms. He has called on the rebels to declare a unilateral ceasefire, and insists rebel leaders must serve prison time. Zuluaga has the backing of Marta Lucia Ramirez, the Conservative party candidate who received 15.5 percent in the first round, although a majority of lawmakers from her party have thrown their weight behind Santos. As finance minister, Zuluaga was credited with bringing growth to Latin America's fourth-largest economy even as the global financial crisis battered other emerging markets. He and Santos share the same basic economic policy ideas of developing natural resources and bringing in foreign investment. (Reporting by Julia Symmes Cobb and Helen Murphy in Bogota, editing by Kieran Murray, Chizu Nomiyama, Mohammad Zargham, Matthew Lewis, Peter Galloway and Eric Walsh)