Senegal should hold presidential elections as soon as possible, the African Union (AU) said, days after its President Macky Sall delayed the February 25 vote to an unspecified date.

Senegal has never delayed a presidential election, and Sall's announcement on Saturday pitched the country into uncharted constitutional waters that some opposition and civil society groups said amounted to an "institutional coup".

AU Commission Chairperson Moussa Faki Mahamat said in a statement late on Sunday that Senegal should "organise the elections as soon as possible, in transparency, peace and national harmony".

"It (AU) strongly encourages all political and social forces to resolve any political dispute through civilized consultation, understanding and dialogue..," the statement added.

Senegal's lawmakers are due to debate on Monday a proposal to hold the vote on August 25 and keep Sall in power until his successor is installed, according to the text of a bill seen by Reuters.