The military junta that seized power in Guinea-Bissau last week has proposed a two-year timeframe for organising new elections, prompting crticism from neighbouring West African states calling for the immediate return of constitutional rule.
The Economic Community of West African States (ECOWAS) "strongly condemns this illegal initiative," a statement said following the announcement that a failed presidential candidate was chosen to lead the two-year transition.
The opposition and military rulers appointed Manuel Serifo Nhamadjo, a former parliamentary speaker and independent presidential candidate, to lead the interim government, in an accord signed late on Wednesday, without the participation of the country's ruling party.
"This [accord] will allow us to peacefully organise voter registration in a biometric format, and to hold legislative and presidential elections simultaneously," said Artur Sanha, a spokesman for the political parties.
On Thursday, the junta also ordered the re-opening of the country's borders, as well as its international airport and sea port, which were closed following the April 12 coup.
Thursday's statement by ECOWAS said: "[The] Commission has learnt with surprise the announced establishment of a so-called 'Transitional National Council' by the Military Command Junta and 24 political parties in Guinea-Bissau to govern the country for a two-year period."
The statement added the junta had given a written undertaking after a meeting with a high-level ECOWAS delegation in Bissau, the capital, to step aside and pave the way for the immediate return to constitutional normality.
The delegation, made up of ministers and chiefs of staff, visited Bissau on Monday to meet those responsible for the coup.
"The Commission wishes to reiterate its rejection of the usurpation of power by the Military Command, and to make it known that it will never recognise any transitional arrangement emanating from the Junta," the statement said.
ECOWAS is due to hold an emergency summit next week to discuss the situation in Guinea-Bissau, it added.
The African Union suspended Guinea-Bissau following the coup.
The World Bank and the African Development Bank have suspended millions of dollars of aid to Guinea-Bissau, raising pressure on the coup leaders to hand back power to civilians.
Elsewhere on Thursday, Portuguese-speaking nations called on the UN Security Council to back an international peacekeeping force for the country, which was colonised by Portugal.
Speaking on behalf of Portuguese speaking nations, Georges Chikoti, Angola's foreign minister, urged the UN Security Council to support a peacekeeping force and step up sanctions against the coup leaders.
"Time is of the essence. We cannot afford to wait and let the people, who are at the mercy of military power, suffer," Chikoti told a council meeting on Guinea-Bissau.
The Portuguese-speaking nations and ECOWAS are already discussing the makeup of a force, diplomats said.
The International Committee of the Red Cross said on Thursday it had brought medical supplies twice to Carlos Gomes Junior, Guinea-Bissau's diabetic former prime minister, since he was detained in last week's military coup.
Gomes Junior had been widely expected to win a presidential election runoff that had been scheduled for April 29 until it was pre-empted by the coup.
He is being held alongside Raimundo Pereira, the interim president, by the ruling junta.
Since gaining independence in 1974, Guinea-Bissau's army and state have remained in constant conflict, and no president has completed a full term in office. Three have been overthrown and one assassinated.