Cardinal Peter Turkson, seen by some as a candidate to become the first African pope in about 1,500 years, has abruptly offered his resignation from a key Vatican department, sources familiar with the matter said on Saturday.

The 73 year old from Ghana, has been a key adviser to Pope Francis on issues such as climate change and social justice, and is the only African to head a Vatican department.

Atiewin Mbillah-Lawson reports