TUNIS (Reuters) - Britain has doubled its contribution to the African Development Fund (ADF), paying $863 million to underpin projects in the continent's poorest countries, the African Development Bank said on Wednesday.

The payment to the Tunis-based bank's soft lending arm is the biggest ever made by the UK which urged other donor countries to follow its lead.

"I very much hope that other shareholders will raise the ambition and also pledge contributions to the replenishment consistent with the needs of Africa today," AfDB President Donald Kaberuka said in a statement.

Donors are due to meet in London next month to agree on an action plan for the 11th replenishment of the African Development Fund.

The African Development Bank has received $5.4 billion to finance projects in infrastructure, the private sector and human development over the three past years, the bank said.