U.S. Secretary of State Rex Tillerson said on Thursday that more African nations should apply “concrete diplomatic and economic pressure” on North Korea in order to achieve denuclearization on the Korean Peninsula.

Speaking at a joint news conference with African Union (AU) Chairman Moussa Faki, Tillerson said the goal of the global maximum pressure campaign, supported by multiple U.N. Security Council Resolutions, was to motivate North Korea to achieve “the complete verifiable and irreversible denuclearization of the Korean Peninsula.”

Tillerson, a former Exxon chief executive, travels to Chad, Djibouti, Ethiopia, Kenya and Nigeria this week on his first trip to Africa as the top U.S. diplomat, seeking to bolster security alliances on the continent.

The top U.S. diplomat may also seek to smooth relations after U.S. President Trump reportedly dismissed some African nations as “shithole countries” in January. Trump later denied making the comment.