QUITO, Feb 6 (Reuters) - Ecuador said on Tuesday it would file a lawsuit charging Colombia with violating an agreement over fumigation of illegal drug fields along their border.

Colombia's U.S.-backed anti-drug program has fueled tensions with Ecuador's new left-wing leader, Rafael Correa, who complains the herbicides pose a risk to residents and farming crops on Quito's side of the porous border.

Correa, an ally of Venezuela's President Hugo Chavez and a critic of U.S. policies in the region, in January agreed with Colombia to monitor the spraying to make sure glyphosate herbicides did not cross over the frontier.

"We know that yesterday fumigation restarted ... they did not inform us and that really complicates matters," Ecuador's Foreign Minister Maria Espinosa told a local television station.

An official at the Colombian Embassy in Quito said he had no immediate comment.

Espinosa said Colombia's actions made it necessary for Ecuador to push ahead with plans to sue Colombia in the International Court of Justice in The Hague, Netherlands, and the Inter-American Commission of Human Rights.

Ecuador in December recalled its ambassador from Bogota after tensions escalated between the South American neighbors over the drug spraying. Bogota says the herbicides are safe.

Colombian President Alvaro Uribe, who has received millions of dollars in U.S. aid to fight the drug trade and left-wing rebels, says the aerial spraying is vital to its efforts because of the security risks in other forms of eradication.

Colombia is the world's top cocaine producer with output of about 600 tonnes of the drug a year. Most of that is shipped to U.S. and European markets.

Uribe's government halted herbicide spraying in a 6-mile (10-km) swathe near the border a year ago after Ecuador and rights advocates complained about the impact on local residents and legal crops.

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