Non-governmental groups in Africa have launched a bid to prevent Sudan's president from becoming chairman of the African Union.

In a letter to African leaders, more than 40 such groups said giving the chairmanship to Sudan would undermine the AU's credibility and jeopardize peacemaking efforts in Sudan's Darfur region.

The letter called Darfur's humanitarian situation "one of the worst in the world." and said Sudanese President Omar al-Bashir cannot be trusted to lead a continental peace initiative.

The African Union is expected to vote on the issue at its summit next week in Khartoum. The organization is currently chaired by Nigerian President Olusegun Obasanjo.

Traditionally, the country that hosts the annual AU summit assumes the chairmanship. But that tradition was broken last year when Nigeria continued for a second 12-month term.

Some information for this report was provided by Reuters.