BOGOTA, Colombia—Colombia's government has ended a nearly monthlong ban on coal shipments by the U.S. -based Drummond Co. that was imposed after it dumped tons of coal into the ocean at a Caribbean port.

The Environment Ministry said Friday that an investigation expected to lead to sanctions would continue into the Jan. 12-13 incident, in which an unspecified amount of coal was dumped into the ocean during rough weather.

The ministry imposed the ban Feb. 6, demanding a new contingency plan from Drummond.

Drummond produces 24 million metric tons of coal in Colombia from an open pit mine near the Caribbean and moves the coal by train to a port near Santa Marta. It is the South American country's No. 2 producer of coal, accounting for nearly a quarter of output.