US President Donald Trump has announced a one-time $90 payment for more than 20 million Medicare beneficiaries, adding to a series of financial proposals and payments unveiled ahead of the November midterm elections.

The White House said the payment will help eligible seniors cover their Medicare Part B premiums and will be funded through the Medicare Improvement Fund, which contains about $2 billion. Most eligible beneficiaries are expected to receive the money through direct deposit, while others will receive checks by mail.

The announcement comes weeks before Americans vote in the November 3 midterm elections and follows Trump's earlier announcement of $500 refunds for nearly one million people enrolled in Affordable Care Act plans.

Trump has also renewed his promise to provide a $5,000 payment to every adult American if Republicans retain control of both chambers of Congress after the elections. That proposal would require congressional approval and could cost more than $1 trillion, according to estimates reported by The Associated Press.

The administration has presented the Medicare payment as an effort to reduce healthcare costs for older Americans. However, Democrats have questioned the timing of the payments and raised concerns about the use of federal funds for the initiative.

Trump has defended the payments as part of his broader effort to put money back into the hands of Americans, while the latest announcement has drawn attention because of its proximity to the midterm elections.

The Medicare payments are expected to begin reaching eligible beneficiaries in early October.