The UN and the US are condemning the forced resignation of Malian Prime Minister Cheick Modibo Diarra, which Washington called a "setback" in the West African nation's efforts to restore democracy.

Diarra quit Tuesday under pressure from influential former putschists opposed to a military intervention to drive out Islamists occupying the northern half of the country and imposing a brutal interpretation of sharia law.

The troubled West African nation's interim president, Dioncounda Traore, swiftly appointed Diango Cissoko to replace Diarra and promised a new government by the end of the week.

"We condemn this act by the military junta and insist that it halt its continued interference in Malian political affairs and government," State Department spokeswoman Victoria Nuland said.

Nuland said the events illustrated "the need to get as quickly as possible to free and fair elections, ideally by April 23rd or as soon as it's technically feasible."

The UN Security Council also decried Diarra's arrest and renewed a threat to impose sanctions against those hampering "constitutional order."

UN Secretary-General Ban Ki-moon also said he was "troubled" by the new turmoil in the African nation.

The Security Council said the action contravenes repeated UN calls for the Malian military to stop interfering in the west African nation's transition.

The 15-nation body stressed its "commitment to authorizing as soon as possible the deployment of an African-led international support mission in Mali."

France is drawing up a resolution giving a mandate to an international force. But negotiations have been prolonged by US opposition to sending just an African-led force to Mali.

The French foreign ministry said the former junta in coup-wracked Mali must stop meddling in politics.

"These developments underline the need to deploy an African stabilisation force," foreign ministry spokesman Philippe Lalliot said.

EU foreign policy chief Catherine Ashton adopted a less condemnatory tone, calling on Mali to appoint a new prime minister acceptable to all sides and urged the military to cease interfering in political life.

With the EU preparing to send a military training mission to Mali aimed at helping it regain control of the north, Ashton called on the interim president to appoint a new prime minister and an inclusive government quickly.

Mali also needs a roadmap to restore constitutional government and provide for new elections, she reiterated in a statement, with the army and security forces coming under civilian control.

She pressed for launching a mechanism and a strategy for reunification through dialogue, adding that the military had to stay out of politics and support the return to constitutional governance.

On Monday, EU foreign ministers approved plans to deploy an EU military training mission of some 250 troops to help the government regain control of the vast semi-desert north from extremist rebels.

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