West Africa's regional bloc has appealed for unity after emergency talks on the political crisis in Senegal and the withdrawal of three coup-hit countries from the group.

The Economic Community of West African States (ECOWAS) extraordinary session on Thursday addressed President Macky Sall's decision to delay elections in Senegal just a week after Burkina Faso, Mali and Niger declared their departure.

ECOWAS commission president Omar Alieu Touray called the turmoil in Senegal a "worrying development".

The chairman of the bloc's Mediation and Security Council Yusuf Maitama Tuggar urged the three countries not to leave, warning their exit would "bring more hardship and do more harm to common citizens".

"We are stronger together as a community," Tuggar, also Nigeria's foreign minister, said as West African foreign and defence ministers attended the council meeting in Nigeria's capital Abuja.

But it was still unclear on Friday what measures -- if any -- the bloc had decided to take.

The draft ECOWAS agenda for the Thursday meeting had listed Senegal's crisis and the departure of the three countries as items for discussion.

- Post-coup suspensions --

Council members held private talks before they returned more than six hours later on Thursday, ending the session without a clear statement on what they had decided.

But after the meeting, Touray told AFP the council had not discussed the constitutionality of Senegal's election delay, which would be a step to imposing sanctions.

"We have to determine the constitutionality or unconstitutionality of an action before any decision to take or impose sanctions," he said.

"That has to be done, and we have not discussed that."

A final statement was expected later on Friday.

The bloc has imposed trade sanctions against Mali and Niger following their coups, but experts had said the prospect of ECOWAS sanctioning Senegal was remote.

Senegal's ministers attended the meeting, but representatives for Burkina Faso, Mali, Niger and Guinea, all temporarily suspended from ECOWAS following coups, were not present.

Touray urged the bloc to remain united, saying "if there is a time for ECOWAS to stay together, this is the time".

Burkina Faso, Mali and Niger announced their intention to permanently withdraw from ECOWAS last month, worsening a diplomatic headache for the bloc, which up until then had 15 members.

The three have said they intend to leave immediately, despite ECOWAS's requirement that countries wait a year before quitting.

- Crisis in Senegal -

Senegal plunged into its worst political crisis in decades this weekend when Sall postponed the February 25 vote to December just hours before campaigning was set to begin.

Lawmakers voted almost unanimously in favour of the delay on Monday, but only after security forces stormed the chamber and removed some opposition members, who were unable to vote.

Observers expressed concern at events in one of ECOWAS's most influential and stable members, raising fears of knock-on effects in the region.

ECOWAS, the United States and European Union have urged Senegal to return to its election timetable, but critics have questioned the regional bloc's sway over increasingly defiant member states.

In a statement on Tuesday, ECOWAS cautioned Senegal against jeopardising "peace and stability" during difficult times for West Africa -- but it was not clear what the bloc would do if Sall defied its warning.

The turmoil has also brought the almost 50-year-old bloc's broader role into doubt -- especially after its warning of a potential military intervention in Niger last year fizzled out with no sign the country's toppled president is closer to being restored.