Postmaster General Louis DeJoy said he would reverse operational changes that critics say would hamper postal voting.

The U-turn comes as Mr DeJoy is due to testify to Congress and at least 20 states were preparing to sue.

There is a fierce debate over postal funding in 2020, as record numbers of Americans are expected to vote by mail due to the pandemic.

The US Postal Service (USPS) under Mr DeJoy had begun what it said were cost-cutting measures in recent months.

Policies that were begun under Mr DeJoy included removing mail boxes, cancelling delivery runs and closing down sorting centres.

In a sharp reversal, Mr DeJoy has now said that post office hours would not be cut, and post boxes and sorting machines would stop being removed.

Mr DeJoy, a former Republican donor, also said overtime pay would continue to be approved to ensure deliveries arrive on time.

"To avoid even the appearance of any impact on election mail, I am suspending these initiatives until after the election is concluded," Mr DeJoy said in a statement.

A week ago, Donald Trump said he had no interest in any additional funding for the US Postal Service, lest the money be used to help process mail-in voting. It was all part of his ongoing, and largely unfounded, campaign against the expanded use of postal ballots to minimise the risk of spreading coronavirus.

By this Monday, the president tweeted that he wanted to "save the post office" and told a crowd in Minnesota that he would "strengthen" the service.

And now, his postmaster general has said the agency will stop taking out postal boxes and limiting delivery routes.