Officials from Washington and Spain announced Monday that they have reached an agreement in principle pertaining to the U.S. cleanup and removal of land contaminated by plutonium-based radiation after a mid-air collision led to undetonated nuclear bombs falling on a site in southern Spain.

A statement of intent signed by Foreign Minister José Manuel García Margallo and U.S. Secretary of State John Kerry states the two sides "intend to negotiate a binding agreement for a cooperative effort to conduct further remediation of the Palomares site and arrange for disposal of the contaminated soil at an appropriate site in the United States," The Miami Herald reported. 

Margallo said during a joint press conference in Madrid that the process would begin soon but failed to go into detail.

The contamination stems from an incident that took place on Jan. 17, 1966, when a U.S. B-52 bomber carrying four nuclear bombs crashed into a tanker plane during a mid-air refueling operation, causing two of the bombs to drop near the Spanish village of Palomares, according BBC News.

The two bombs didn't detonate, but did end up breaking apart and spreading seven pounds of plutonium over a .76 square-mile area. The third bomb equipped with a parachute landed intact, while the fourth landed five miles off-shore and was later recovered by the USS Petrel.

Washington had paid $350,000 a year to monitor radioactivity levels, following an earlier accord that ended in 2010, while also conducting regular blood tests for more than 1,000 Palomares residents, according to AFP.

The agreement comes close to the 50-year anniversary of the incident, which is considered one of the most serious nuclear incidents of the Cold War.