The African Union, the EU and former colonial power France have all rejected a call by Tuareg rebels in north Mali for their newly named region of Azawad to be recognised as independent.
The National Movement for the Liberation of Azawad (MNLA) seized the area last week.
The MNLA is one of two rebel groups to have gained ground in the area after Mali's government was ousted in a coup.
The other, the Islamist Ansar Dine, says it wants no part in the MNLA move.
The head of the African Union, Jean Ping, said the MNLA announcement had no value whatsoever.
The European Union demanded negotiations to solve the crisis, with Maja Kocijancic, the spokeswoman for EU foreign affairs chief Catherine Ashton, telling Agence France-Presse: "The EU has made clear throughout the crisis that it respects the territorial integrity of Mali."
French Foreign Minister Alain Juppe also said that Paris insisted on Mali's territorial integrity and rejected the MNLA appeal.
Defence Minister Gerard Longuet added: "A unilateral declaration of independence that was not recognised by African states would have no meaning."
Britain announced it was closing its embassy in the capital, Bamako, and withdrawing its staff.
AFP also quoted Ansar Dine's military chief Omar Hamaha as saying the group wanted no part of the MNLA announcement.
"Our war is a holy war. It's a legal war in the name of Islam. We are against rebellions. We are against independence. We are against revolutions not in the name of Islam," Mr Hamaha said.
Ministers from three of Mali's neighbours, Algeria, Mauritania and Niger, are reported to be meeting in Nouakchott, Mauritania, on Sunday to discuss the crisis.
A 2,000-strong force has been put on standby by the Ecowas regional grouping.
It is waiting for a response from regional heads of state before deploying the force.
The crisis was sparked when Mali's army seized power on 22 March, accusing the elected government of not doing enough to halt the two rebel groups.
Rights group Amnesty International has warned that Mali is on the brink of a major humanitarian disaster in the wake of the rebellion.
The MNLA had declared its "unilateral" ceasefire on Thursday after the UN Security Council called for an end to the fighting in Mali.
A statement posted on the rebel website on Friday proclaimed independence, adding it would respect existing borders with neighbouring states and adhere to the UN Charter.
"We completely accept the role and responsibility that behoves us to secure this territory.
"We have ended a very important fight, that of liberation... now the biggest task commences," rebel spokesman Mossa Ag Attaher is quoted as saying by AFP.
The Tuareg people inhabit the Sahara Desert in northern Mali, as well as several neighbouring countries and have fought several rebellions over the years.
They complain that they have been ignored by the authorities in Bamako.
Mali has been in disarray ever since the coup, with people continuing to flee the northern areas.