By Hugh Bronstein

BUENOS AIRES (Reuters) - Argentina extradited an alleged Colombian drug kingpin known as "My Blood" to the United States on Thursday to face charges of organizing cocaine shipments.

Henry de Jesus López, whose nickname is "Mi Sangre" in Spanish, was captured by Argentine police in 2012 at his favorite restaurant in the Buenos Aires suburb of Pilar, where he lived after fleeing his homeland.

He was turned over to U.S. marshals early on Thursday, Argentina's security ministry said in a statement.

The decision to send Lopez to face trial in Florida comes at a time of improving diplomatic relations and security ties between Argentina and Washington.

Lopez, 45, once key underworld figure in the Colombian city of Medellin, slipped into Argentina in 2011 with a forged Venezuelan passport. He has been charged in U.S. federal court with managing smuggling routes through which tonnes of cocaine left Colombia's Atlantic coast bound for the United States.

He had risen to prominence after Medellin's previous crime boss Diego Fernando Murillo, alias "Don Berna", was extradited to the United States along with other leaders of Colombia's right-wing paramilitary groups.

Lopez was also a leader of Colombia's paramilitary movement, which started as a way of protecting land owners from left-wing guerrillas now trying to close a peace deal with the government. Both armed groups ended up in the cocaine business.

Lopez also faces cocaine charges in Colombia, which often extradites suspects wanted by the U.S. courts to the United States.

Other Colombian traffickers are thought to be hiding in Argentina, which has become an export hub for cocaine smuggled into the country from the Andean region.

The extradition comes at a time of improving ties between Washington and Buenos Aires after center-right Argentine President Mauricio Macri was elected a year ago on promises of improving the economy, in part by attracting U.S. investment.

Since then, Argentina has been visited by President Barack Obama and Secretary of State John Kerry after years of icy relations under previous leftist leader Cristina Fernandez.

Macri is one of the few Latin American leaders to have called Donald Trump since the Republican businessman won the U.S. presidential election last week.

(Reporting by Hugh Bronstein; Editing by Frances Kerry)