Veteran US diplomatic troubleshooter Bill Richardson launched Wednesday a mission to Cuba to free an American contractor whose prolonged detention has blocked efforts to improve bilateral relations. Alan Gross, 62, an independent contractor employed by the State Department, was arrested in December 2009 and sentenced in March to 15 years in prison for violating "the independence or territorial integrity" of Cuba. Washington dismisses the espionage charges and says Gross was bringing satellite phones and other equipment to Cuba's Jewish community while working for the US Agency for International Development's democracy-building program. State Department spokeswoman Victoria Nuland said that while Richardson was traveling to Havana as a "private citizen," the US government supported his efforts to free Gross. There was no information on his meetings in Cuba. A spokesman for the 63-year-old former New Mexico governor, who has also served as energy secretary and US ambassador to the United Nations, confirmed that Richardson was in Cuba but gave no details of his program. The Gross case heightened tensions between Washington and Havana just as President Barack Obama's administration leaned towards rapprochement after relaxing some decades-old economic sanctions against Cuba in January. Raul Castro took over from elder brother Fidel as head of the ruling Communist Party during April's Congress. He assumed the responsibilities of president in 2006 due to his brother's illness. Obama has called on Raul Castro to institute real democratic reforms if he wants a normalization of relations, but despite the release of dozens of political prisoners in recent months the pace of change has been slow. Cuba claims that the United States continues to imprison five Cuban anti-terrorist agents who were convicted of espionage in 2001. Havana considers the "Cuban Five" political prisoners and says their aim was not to spy on the US government but to gather information on "terrorist" plots by Cuban expatriates in Florida, a bastion of anti-Castro fervor. Richardson is aiming to fare better than former US president Jimmy Carter, who traveled to Havana and met both Fidel and President Raul Castro in March but failed to secure Gross's freedom. The contractor has lost some 40 kilograms (90 pounds) in jail, according to his wife Judy, while his daughter and mother-in-law are battling cancer. Carter's three-day trip was a private visit at Havana's invitation, aimed at improving US-Cuban relations. As the only sitting or former US president to meet with the communist leadership in its 52-year rule, his mission carried considerable political weight in Cuba but failed to produce concrete results. Richardson, a high-profile Democratic politician who served as energy secretary under former US president Bill Clinton, has undertaken several high-profile diplomatic missions in the past. Arguably the highest-profile Hispanic politician in the United States, he was on the short-list to be Obama's secretary of state before the job went to Hillary Clinton. He made his name as the "Indiana Jones" of US diplomacy and is famed for daring head-to-head encounters with strongmen leaders on the US pariah list, including Iraq's late president Saddam Hussein and Cuba's Fidel Castro. Over the years Richardson has emerged as a favored go-between for North Korea's Stalinist regime in successive nuclear showdowns with Washington, and was most recently in Pyongyang in December 2010. The Cuban government rejected a US decision in August to keep it on its blacklist of countries that allegedly support terrorism and accused Washington instead of sheltering the "real terrorists."