The charter would aim to make it easier for power to change hands through the ballot box, but a BBC correspondent says some clauses are contentious.

Several leaders have tried to overturn constitutional bans on presidents serving more than two terms in office.

The AU is already supposed to suspend governments which take power by arms.
A final version is expected to be put to African heads of state at their annual summit meeting this weekend.

The BBC's Elizabeth Blunt says the proposed charter is a strongly worded document, considering the personal histories of some of the men who will be asked to approve it.
The host of this meeting, Gambian President Yahya Jammeh, like several of his peers, is a former soldier and coup-maker who later legitimised his rule through an electoral process.

The most senior of the AU leaders, Omar Bongo, has been president of Gabon since before many of the participants in this summit were even born.

Controversial
If adopted, the new charter would condemn any unconstitutional change of power, as well as any refusal to accept defeat and hand over power after losing an election.

This much, as well as the threat of suspension from the Union for offending governments, seems likely to be accepted by the summit.

The attempt last year by the young Togolese President Faure Gnassingbe to step into his dead father's shoes without an election was greeted with general disapproval across the continent and he was ostracised in just the way proposed in the new charter.

Mr Faure stepped down after being proclaimed president but won disputed elections shortly afterwards.

More contentious has been a clause condemning attempts to change the constitution in order to stay in indefinitely in power.

This is a live issue in several countries, including Uganda, and Nigeria, where heads of state have changed or have shown signs of wanting to change their constitutions to extend the presidential term.

The proposed charter has strong support from the head of the African Union commission, Alpha Omar Konare, who in his opening address to the meeting, called for clear political engagement to bring this charter into force.