The government has denied delaying the process of receiving another 1 million doses of Pfizer vaccines against Covid-19 to be donated by the US.

The move comes after politician Khunying Sudarat Keyuraphan visited Thai-born US senator Tammy Duckworth in Washington, DC on Wednesday.

Ms Duckworth helped to arrange the donation of 2.5 million doses for Thailand.

A total of 1,503,450 doses of Covid-19 vaccine manufactured by Pfizer-BioNTech were delivered to Thailand on July 30.

The US embassy previously confirmed the United States will provide an additional one million doses.

During the conversation with Khunying Sudarat, Ms Duckworh was reported to have said: "All I can tell you is that I've been advocating for Thailand to get more vaccines ... and Thailand has a million doses waiting to go.

"But because Thailand has not finished the paperwork ... I know I told the ambassador a month ago that it needs to be completed. They said OK, they're going to work on it.''

The Thai government has not yet sent documents to inform the US of its intention to accept the vaccines, so the US still could not deliver them, Khunying Sudarat quoted her as saying.

In response, Public Health Minister Anutin Charnvirakul said the Foreign Affairs Ministry had not received any documents from the US.

Department of Disease Control director-general Opas Karnkawinpong echoed this response.

"Since the first donation, the US still has not yet notified the ministries that it will donate any additional vaccine doses," Dr Opas said.

"Therefore, the report that Thailand has denied or failed to respond to the donation is not true."