Ecuador broke off diplomatic ties with Colombia in 2008 after a Colombian bombing raid on a FARC guerrilla camp on the Ecuadorean side of the border. Relations were partially restored in November, but not to the level of ambassador.

Agents of Colombia's DAS intelligence service tapped telephone conversations of Correa and his top officials after the 2008 raid, an Ecuadorean newspaper reported on Monday.

"It would not only be an obstacle to the re-establishment of bilateral relations. We would have to go back and break relations. This is extremely serious," Correa told reporters.

Colombia had no immediate comment on Correa's statement.

The two countries currently have lower level diplomats or charges d'affaires in place and had held encouraging talks in recent months about restoring full relations.

Colombia's Administrative Security Department, known by its Spanish initials DAS, denies the accusation of spying. The charge is being investigated by Correa's government.

The DAS has been hit by a string of scandals, including allegations of illegal wiretapping of judges, journalists and opposition politicians in Colombia.

The United States cut off aid to the agency amid charges that Uribe's advisers directed some of the abuses from the presidential palace. Uribe has said his government will disband the DAS and create a smaller, better-controlled agency.

*Reporting by Santiago Silva, editing by Anthony Boadle