Mali's military junta has said it may charge ousted President Amadou Toumani Toure with high treason and financial misconduct following March's coup.
Putsch leader Capt Amadou Sanogo also called for a "national meeting" on the country's future as international sanctions begin to hit.
Landlocked Mali has to import all its fuel and in the capital long queues have formed at petrol stations.
Following rebel advances in the north, some aid groups have stopped work.
Renegade officers deposed President Toure last month saying he had not done enough to fight Tuareg rebels, who began their rebellion in January.
Since the military took charge, the rebels have made significant territorial gains in northern Mali - including taking the World Heritage Site of Timbuktu over the weekend.
International pressure is growing on the coup leaders and correspondents say the country will struggle to survive an economic blockade.
The International Committee for the Red Cross told the BBC it had suspended most of its operations in the north and temporarily withdrawn its international staff after its warehouse in Gao was looted by Tuareg rebels.
According to the UN refugee agency, since January the violence has uprooted more than 200,000 people, including around 100,000 who have fled the country.
The coup and Tuareg rebellion have also exacerbated a humanitarian crisis in Mali and some neighbouring countries, with aid agencies warning that 13 million people need food aid following a drought in the region.
"The overall security situation really deteriorated over the weekend," Steven Anderson, spokesman for the Red Cross in North and West Africa, said.
"This is extremely regrettable because this food and other emergency items, such as blankets, such as hygiene material, were meant for tens of thousands of displaced people inside northern Mali that are really now living in very dire conditions," Mr Anderson said.
A spokesman for the Catholic chartiy Caritas told the BBC that its office in Gao and a local church were destroyed by the rebels, some of who are Islamists.
Ryan Worm said about 200 Catholics had gone into hiding - and most Gao residents are trying to stay indoors since the rebel takeover.
Ahead of Thursday's national meeting, an association of northern people, who live in the southern capital Bamako, are meeting to discuss the situation in the north.
The heads of Mali's Catholic and Muslim communities are also travelling to Burkina Faso to meet with President Blaise Compaore, who has been appointed as the mediator in Mali's crisis.
"We call the entire political class and all civil society actors to... a national meeting which will begin on April 5," Capt Sanogo told journalists.
He said the meeting on Thursday would determine "what will be best for the country in a consensual, democratic fashion".
He added that the ousted president "could be the object of judicial proceedings for high treason and financial wrongdoing", without giving more details.
The rebels are divided into two groups - the National Movement for the Liberation of Azawad (MNLA), which wants independence for the northern Tuareg homelands, while Ansar Dine, which is linked to the North African branch of al-Qaeda, wants to remain part of Mali but impose Sharia.
The US, a former key ally of Mali, has expressed concern that the political crisis is allowing radical Islamists to gain ground, and threatening the country's territorial integrity.
There have been reports of extremist Salafi groups moving into towns in the north taken over by Tuareg rebels in recent days.
Residents in Gao and Kidal told the BBC that Islamist fighters have ransacked bars serving alcohol and banned Western music on local airwaves.
In Timbuktu, people told the BBC that Ansar Dine members are going from door-to-door telling occupants that they now have to live by the principles of Islamic law.
"The United States urgently calls on all armed rebels in the north of Mali to cease military operations that compromise the Republic of Mali's territorial integrity," US State Department spokeswoman Victoria Nuland said.
Some civilians are reported to be fleeing the central towns of Mopti and Sevare fearing a rebel advance further south.
On Monday, Mali's West African neighbours imposed tough economic sanctions, including the closing of the country's borders and the freezing of its account at the regional central bank.
The African Union and the US have now also imposed targeted sanctions on the coup leaders and anyone actively supporting them, including travel bans and asset freezes.
The UN Security Council is expected to release a statement on the crisis on Wednesday.