African leaders agreed to form a $3 trillion continental free-trade zone encompassing 1.2 billion people, but its two biggest economies, Nigeria and South Africa, did not sign up, diminishing its impact.

The African Union started talks in 2015 to establish a 55-nation bloc that would be the biggest in the world by member states, in a bid to increase intra-regional trade, which sits at a measly 15 percent of Africa's total commerce.

Rwandan President Paul Kagame, host of an AU summit called to conclude the initial negotiations, declared the meeting a success on Wednesday after 44 African nations signed up to establish the free-trade bloc within 18 months.