West Africa's ECOWAS and African Union observers on Wednesday expressed concern over the military takeover in Guinea-Bissau and the arrests of election officials, a joint statement issued by the organizations said.

A group of army officers said earlier on Wednesday they had seized power in the coup-prone West African nation, a day before the planned announcement of results from a hotly contested presidential election.

"It's regrettable that this (coup) announcement came at a time when the missions had just concluded meeting with the two leading presidential candidates, who assured us of their willingness to accept the will of the people," the observers said.

The observer missions that included Mozambique's former President Filipe Jacinto Nyusi and Nigeria's former President Goodluck Jonathan, called on the regional bodies to take the necessary steps to restore constitutional order.

"We urge the armed forces to immediately release the detained officials to allow the country's electoral process to proceed to its conclusion," the statement from the Economic Community of West African States and African Union observers said.