Rebels in Mali have captured the northern town of Kidal, just a week after the military seized power saying the army needed more equipment to fight the insurgents.
A rebel spokesman told the BBC they were in charge of the town, which local residents confirm.
As the news was coming through, coup leader Capt Amadou Sanogo asked for foreign help to tackle the rebels.
The coup has been condemned - Mali's neighbours have threatened sanctions.
On Thursday, West African nations gave Mali's military leaders 72 hours to relinquish power.
The regional body, the Economic Community of West African States (Ecowas), said the proposed measures included closing land borders, freezing Mali's assets and a financial blockade.
The leaders met in Ivory Coast, after earlier plans for talks with the coup leaders in the Malian capital, Bamako, were abandoned as coup supporters occupied the airport's runway.
Mali's neighbours have also placed a peacekeeping force on standby.
Queues at banks
Kidal is the largest of several northern towns the rebels have seized in recent months.
The fighter from the National Movement for the Liberation of Azawad (MNLA) told BBC Afrique: "[Kidal] is totally controlled [by us], there is no more resistance, all army positions have fallen."
Azawad is the Tuareg name for their home region in the Sahara Desert - Tuaregs have launched several rebellions over the years, complaining that the government based in far-off Bamako was ignoring them.
The latest insurgency was launched last year after Tuareg fighters returned from Libya where many had supported the late Libyan leader Muammar Gaddafi.
Capt Sanogo told journalists in Bamako that the situation was "critical".
"Our army needs the help of Mali's friends to save the civilian population and the Mali's territorial integrity," he said.
But he was speaking after Mali's neighbours had threatened to effectively strangle the country unless the military leaves power.
The president of the commission of Ecowas, Kadre Desire Ouedraogo, told reporters on Thursday that if the 72-hour deadline was not met, all the 15 countries of the bloc would deny Mali access to their ports, and there would be no transfers to commercial banks in Mali from the regional central bank, based in Senegal.
Mali is one of eight West African countries which use a common currency - the CFA franc.
The BBC's John James in Ivory Coast says it is difficult to see how the regime in poor, landlocked Mali could cope if these sanctions were imposed.
He says the financial isolation of the government of then Ivory Coast President Laurent Gbagbo played a key role in weakening his grip on power last year - and he was in a far stronger position than coup leader Capt Amadou Sanogo.
Journalist Martin Vogl in Bamako told the BBC's Network Africa programme that, even before the deadline was announced, there were long queues of people trying to withdraw money from banks in Mali's capital.
He says people are now likely to stock up on essential goods such as food, as well as petrol, which must be imported.
There has been no official reaction to the deadline from Mali's military rulers but Martin Vogl says they are very angry.
He says many Malians are upset that after 20 years of democracy, the army is once more in charge but there was also growing disillusionment with the ousted government and some feel Ecowas is pushing too hard.
The coup leaders have unveiled a new constitution as well as announcing elections in which those who took part in the coup would be barred from standing. However, no date has yet been set.
Under the new constitution, a transitional committee composed of 26 members of the security forces and 15 civilians would take power.
President Amadou Toumani Toure said on Wednesday that he remained in the country, free and in good health.