Colombia's Ambassador to the United States Carlos Urrutia resigned Tuesday after being accused of involving in a land swindle scandal.

Urrutia said in his resignation letter that he has helped a law firm purchase thousands of hectares of land from peasant farmers in eastern Vichada department at bargain prices and then sold them to multinational firm Cargill.

"The law firm I was head of offered legal advice to companies with agribusiness interests in the high plateau region that are trying to transform the country into a food powerhouse," said Urrutia, who was a major shareholder of the Brigard & Urrutia firm prior to his assignment in Washington.

He claimed his resignation as ambassador was to clear his name of the accusations, made by Jorge Robledo, a senator from the Democratic Pole Party and an outspoken critic of Urrutia.

The senator said the case demonstrated how Colombia's top companies participate into the usurping of land regardless of the country's limits on purchasing private property.

Robledo said Urrutia should have resigned earlier and called on the government to launch an exhaustive investigation into the scandal.

Colombian President Juan Manuel Santos lauded Urrutia's resignation as a "gallant act", saying it showed his desire "not to allow his remaining at the embassy to be used to damage the government and the country."

The president said Urrutia has reasons to be proud of his contribution to the country since being appointed as ambassador a year ago and thanked him on behalf of the Colombians for his work.