BRASILIA, June 22 (Reuters) - Brazilian federal prosecutors have opened an investigation into a contract worth 1.6 billion reais ($320 million) for 20 million doses of a COVID-19 vaccine made by India's Bharat Biotech, according to a document seen by Reuters on Tuesday.

The prosecutor-general's office (PGR) cited comparatively high prices, speedy talks and pending regulatory approvals as red flags for the Bharat contract signed in February, before similar deals with Pfizer Inc and Johnson & Johnson .

Bharat did not immediately respond to a request for comment outside of business hours in India.

The Bharat contract has also drawn scrutiny from a Brazilian Senate inquiry, which called for testimony on Wednesday from the head of Precisa Medicamentos, Bharat's intermediary in Brasilia.

Justifying the preliminary probe, prosecutors flagged in a document dated June 16 that Precisa's partners include Global Saude, a company accused of selling but not delivering medicine to the Health Ministry in a case under investigation by police.

Precisa and Global did not immediately respond to requests for comment.

Prosecutors questioned why the Health Ministry had agreed to buy the Bharat vaccine, which had not cleared regulatory hurdles, for around $15 per dose: significantly more than what it paid for Pfizer's vaccine, which had regulatory approval.

"The history of irregularities involving partners at Precisa and the elevated price paid for the doses under contract ... require deep investigation in both civil and criminal aspects," wrote prosecutors.

In a separate document seen by Reuters, Senate investigators cited testimony from an unnamed public servant describing "abnormal pressures" from senior Health Ministry officials to reach a deal for the Bharat vaccine, branded Covaxin.

In March, Brazilian health regulator Anvisa rejected a request from the government to import doses of Covaxin, citing concerns about Bharat's manufacturing standards as well as a lack of safety data and other documentation. ($1 = 5.0043 reais) (Reporting by Ricardo Brito Additional reporing by Anthony Boadle Editing by Brad Haynes and Jonathan Oatis)