By Peter Loftus and Joseph Walker

AstraZeneca PLC said Thursday it signed new agreements aimed at broadening global distribution of a coronavirus vaccine being developed by Oxford University researchers, after the drugmaker signed supply deals that reserved initial doses for the U.K. and the U.S.

The U.K. drugmaker said it would receive $750 million to manufacture and allocate about 300 million doses for a global distribution system being set up by international foundations as part of one agreement. Under the other deal, AstraZeneca said it would supply one billion doses for low- and middle-income countries.

The company said in total it has secured manufacturing capacity to support production of two billion doses of the Oxford vaccine, which is being tested in clinical trials.

The distribution deals are the latest signed by a drugmaker working on a coronavirus vaccine. The companies have been straddling competing demands from national leaders who want to secure supplies for their own populations and from those who want to set up global allocation systems, including programs to vaccinate health-care workers around the world before the general population.

In the first agreement, the Coalition for Epidemic Preparedness Innovations, an Oslo-based nonprofit that has funded several coronavirus vaccine projects this year, said it is setting up a global development and distribution system for coronavirus vaccines with another nonprofit.

CEPI will lead development and manufacturing, while the other nonprofit, Gavi, will lead procurement. Geneva-based Gavi provides access to vaccines in poor countries.

Under the terms, CEPI will provide $383 million and GAVI will give $367 million, an AstraZeneca spokeswoman said. AstraZeneca will provide the 300 million doses on a "no-profit" basis during the pandemic, CEPI said.

It is still unknown whether the vaccine will prove safe and effective in clinical trials, but it is one of the most promising of more than 50 vaccines reviewed by CEPI, CEO Richard Hatchett said on a conference call with reporters on Thursday.

"We believe the probability of success is high enough that we are willing to support the manufacturing at-risk," Dr. Hatchett said.

AstraZeneca aims to have results of clinical trials of the vaccine in August and begin delivering doses in the U.S. and U.K. in September and October.

That timeline, though, is dependent on having enough clinical trial participants as the rate of new infections slows in many countries, AstraZeneca CEO Pascal Soriot said on the conference call.

"We are chasing the disease in many parts of the world," Mr. Soriot said. "We're doing our very best."

Separately, AstraZeneca said it reached a second agreement with the Serum Institute of India to provide one billion doses for low and middle-income countries, including 400 million by the end of this year. The Serum Institute of India is a major manufacturer of low-cost vaccines for the developing world. Terms weren't disclosed.

Last month, AstraZeneca agreed to provide 100 million doses to the U.K., with an initial supply of 30 million doses as soon as September. Also last month, the drugmaker agreed to receive up to $1.2 billion from the U.S. to secure 300 million doses as early as October.

Initial supplies of any successful vaccine are expected to be limited. Some drugmakers have sought to set up manufacturing capacity in multiple countries, in case individual countries impose export bans on any successful vaccines produced within their borders.

CEPI's Dr. Hatchett said the group will work with the World Health Organization, which will develop guidelines for allocating vaccines.

It is likely that health-care workers and high-risk people such as the elderly and those with pre-existing conditions like diabetes would be prioritized for vaccination, he said. The goal, CEPI said, is to ensure equitable access to Covid-19 vaccines for countries that wish to participate.

The CEPI partnership with AstraZeneca will support the transfer of vaccine-production technology to manufacturing of the doses at sites in Europe.

Write to Peter Loftus at peter.loftus@wsj.com and Joseph Walker at joseph.walker@wsj.com