The letter signed by the Taliban's foreign minister Amir Khan Mutaqi calls on Washington to release Afghan central bank assets.

"Currently the fundamental challenge of our people is financial security and the roots of this concern lead back to the freezing of assets of our people by the American government," the letter released on Wednesday reads.

The Taliban are concerned that if the current situation prevails it will lead to mass migration and damage the country's health and education sectors.

"The suffering of a child from malnutrition, the death of a mother from lack of health services, the deprivation of a common Afghan from food, shelter, medicine and other primary needs has no political or logical justification, and it is detrimental for the prestige of the government and people of the United States of America because this is a pure humanitarian issue," the letter said,

When the Taliban took over power in the country in August, most aid to Afghanistan was suspended.

Around $US9 billion ($A12 billion) in the country's central bank reserves, most of which are parked in the United States, have been frozen.

Prior to that, the Kabul government had received $US8.5 billion in military and civil aid annually, according to a report by the Kabul think tank Afghanistan Analysts Network.

The grants were used to finance 75 per cent of public spending.

Millions of people have now lost their main source of income, and the education and health sectors, as well as other public services, are no longer fully operational.

The United Nations has warned 97 per cent of Afghans could plunge into poverty by mid-2022.

Australian Associated Press