The World Bank has suspended its aid to Sudan, after the military there staged a coup against the civilian government.
Political leaders were arrested on Monday, sparking nationwide protests and international condemnation.
Sudan's civilian and military leaders had been in a fragile power-sharing agreement for the past two years.
The sudden cut to aid is likely to have dire consequences for Sudan's battered economy, at a time when it was just starting to get back on its feet.
The World Bank and AU moves put further pressure on the coup's leader, Gen Abdel Fattah Burhan, to reinstate the civilian government.
Gen Burhan was in charge of the power-sharing agreement, and has said the coup was needed to avoid "civil war". He has insisted that Sudan is still moving towards democracy and elections in 2023 - but his reasoning and the sudden takeover have been widely rejected.
The president of the World Bank, David Malpass, said in a statement: "I am greatly concerned by recent events in Sudan, and I fear the dramatic impact this can have on the country's social and economic recovery and development."
The World Bank has contributed some $3bn in aid to Sudan to support agriculture, transport, health care and education, among other things, according to Prime Minister Abdalla Hamdok.
In a speech last month to the World Bank, he said that changes from the funding "have begun to bear fruits" as the economy showed signs of stabilising. Now, that is at risk again.
The AU tweeted that while it welcomed the release of the prime minister, who was detained on Monday, Sudan will remain suspended from its activities until the civilian government is reinstated.
And the US Secretary of State, Antony Blinken, said he had spoken with Sudan's civilian-allied Foreign Minister Mariam Sadiq al-Mahdi and pledged his support for a return to "a civilian-led transition to democracy".
Late on Wednesday, state media reported that six Sudanese ambassadors had been removed from their posts by the military.
Those withdrawn included the country's representatives to the US, the European Union and China, all of whom have condemned the army's takeover.
Street protests continued for a third day, with at least 10 people killed after soldiers opened fire on crowds. Troops reportedly travelled house to house in Khartoum arresting local protest organisers.
Trade unions representing doctors and oil workers said they were joining the demonstrations, as did staff at the Sudanese Banking Association.
"We stand firmly against any military action and any form of dictatorship," the association's spokesman, Abdul Rashid Khalifa, told the BBC.
The agreement between civilian and military leaders was signed in 2019 after long-time ruler Omar al-Bashir was overthrown. The power-sharing was designed to steer Sudan towards democracy but has proven fragile with a number of previous coup attempts, the last just over a month ago.