KAMPALA, April 3 (Reuters) - Uganda will commission its first tin refining plant in the southwestern region next month, a senior mining ministry official said, as part of efforts to expand capacity and add value domestically to its minerals.

President Yoweri Museveni wants to maximise the benefits of exports to the East African nation, where several gold refineries are operating, and Chinese-backed Sunbird Resources was recently licensed to mine limestone for cement production.

"We are preparing to launch our very first tin processing facility," Irene Bateebe, a top official of the energy and mineral development ministry, told Reuters on Wednesday, adding the launch would take place next month.

Woodcross Resources, a Uganda-based mining and mineral trading company, owns the plant.

"They will be refining tin to over 99% in terms of its purity," Bateebe added, without revealing the size of the investment. Woodcross did not immediately respond to a request for a comment.

On its website, Woodcross says it has a tin mining licence covering 40 square km (15 sq miles) in western Uganda and its tin refining plant has annual capacity of more than 1,000 tonnes. (Reporting by Elias Biryabarema; Editing by George Obulutsa and Clarence Fernandez)