MONROVIA, Sept 10 (Reuters) - ArcelorMittal will triple its iron ore production in Liberia to 15 million tonnes a year during a first phase of an expansion that will see it invest an additional $800 million in the country, Executive Chairman Lakshmi Mittal said on Friday.

He said the company was exploring the possibility of expanding production to as much as 30 million tonnes a year.

Mittal made the comments after the company signed an agreement with the Liberian government that commits ArcelorMittal to staying in Liberia for at least another 25 years. (Reporting by Alphonso Toweh; writing by Aaron Ross Editing by Bate Felix)