India has delayed committing supplies of vaccine to the COVAX global sharing effort, two sources told Reuters on Tuesday, a day after one of its key backers, the World Health Organisation (WHO), said the agency could not "cut corners" to approve a domestically developed vaccine.

The world's biggest vaccine maker resumed exports of Covid-19 doses this month for the first time since April. It has sent about 4 million to countries such as neighbouring Bangladesh and Iran, but none to COVAX.

Delayed supplies to COVAX could disrupt inoculation drives in many African nations that rely on it for vaccines.

On Monday, in the run-up to an October 26 meeting on Covaxin, India's first domestically developed Covid-19 vaccine, the WHO said it could not "cut corners" in the approval decision.

One of the sources said it was "frustrating" that India had yet to confirm any supply to COVAX, despite a promise by the health minister last month to meet the commitment to COVAX and others during the quarter to December.

The sources, who have been briefed on the export talks, declined to be identified as they were not authorised to speak on the subject.

"We are still waiting for confirmation on when and how many doses we can expect when exports do resume, and are not aware of any specific delay," COVAX co-lead GAVI, the Global Alliance for Vaccines and Immunization, said in an email.

"Indian vaccines have a powerful role to play" in ending the pandemic, it added.

India's health ministry, WHO and the Serum Institute of India (SII), which is the world's biggest maker of vaccines, did not respond to requests for comment.

SII, contracted to supply hundreds of millions of doses of a version of the AstraZeneca vaccine to COVAX and countries such as Bangladesh, has more than tripled its output of the vaccine since April, to reach 220 million doses a month.

Indian government officials have said they are confident the WHO will soon approve emergency use of Covaxin, which accounts for 11 percent of the 990 million doses India has injected, with the rest mostly from AstraZeneca.

A few weeks ago, Adar Poonawalla, the chief executive of SII, told the Telegraph newspaper that the company would resume exports to COVAX in October.

"Initially these supplies will be small, but by January 2022, once we have satisfied domestic demands ... we will see large volumes go to COVAX," he added.

Before India halted overseas vaccine shipments in April to fill domestic demand, it donated or sold more than 66 million Covid-19 doses, including Covaxin.