New Delhi, July 1 -- A Colombian senator, who recently lost the nation's presidential election, said Tuesday he will not recognize his opponent, Abelardo de la Espriella, as the nation's new head of state, if he does not comply with several demands, including renouncing his U.S. citizenship.

In a statement issued Tuesday, progressive senator Ivan Cepeda urged de la Espriella, the winner of June's presidential runoff, to renounce his U.S. citizenship, arguing that holding it while being Colombia's president could generate conflicts of interest.

The senator also said that de la Espriella should clarify whether he is an "agent" of the United States, because as a criminal defense lawyer he defended a former paramilitary leader who was an in...