African leaders have backed a "strategy of collective withdrawal" from the International Criminal Court (ICC), but it came with unspecified reservations, an African Union official said on Wednesday after this week's African Union summit.

The official did not give details about the strategy or the reservations, but it highlights broad antipathy towards the court among Africans who feel the ICC unfairly targets them.

A document seen by Reuters before the summit proposed a co-ordinated withdrawal unless the ICC was reformed. It included a call for "regionalisation" of international law, a reference to proposals for an African war crimes court.

Almost a third of the ICC's 124 members are African, and a withdrawal by a large number of them would cripple a court that has yet to fulfil hopes that it would ensure perpetrators of war crimes and genocide never go unpunished.

Three African states - South Africa, Gambia and Burundi - signalled last year their intention to quit what is the world's first permanent global war crimes court.

The ICC, which is 15 years old this year, has only ever charged Africans, including the presidents of Kenya and Sudan, although it has procedures open at earlier stages dealing with crimes in Eastern Europe, the Middle East and South America.

"The leaders of AU member states endorsed the strategy of collective withdrawal, with reservations," the AU official, who asked not be identified, told Reuters.

It was not immediately clear if the agreement reached at the AU summit was the same as the document circulated beforehand.