"I can confirm that we have 7 million releasable doses available of AstraZeneca," Psaki said at Thursday's White House press briefing. "2.5 million of those, we are working to finalize plans to lend those to Mexico and 1.5 million to Canada," she added.

President Joe Biden could announce the agreement upon finalization, which could happen as soon as Friday, CNN has learned. On Tuesday, Mexico's foreign minister said an announcement could come by the end of the week.

"I'd say we've made good progress, but the details, figures, provisions, won't be known until Friday," Mexican Foreign Minister Marcelo Ebrard told reporters on Tuesday morning, according to Reuters. "We requested as many (AstraZeneca doses) as possible."

Biden has met virtually with both Canadian Prime Minister Justin Trudeau and Mexican President Andrés Manuel López Obrador. During the conversations, they both pressed him on the need for more vaccines. Mexican government officials also pressed Biden officials on helping with vaccine supply during conversations between both parties regarding the surge on the southern border, an administration official told CNN.

The Biden administration has committed to having enough vaccines for all Americans before sharing doses, and if this agreement comes together it would be the first time the US has shared vaccines directly with another country. It would also likely give a major boost to vaccination efforts in Canada and Mexico who are struggling with their vaccine roll-out in comparison to the US.

On Wednesday, White House press secretary Jen Psaki confirmed that requests have been received from both Mexico and Canada and said that they are being considered carefully. She provided no details on when a decision would be reached.

The other administration official told CNN that one option under consideration is a swap agreement with the two countries: an agreement to share the AstraZeneca doses now with the condition that Mexico and Canada will share excess vaccines with the US in the future.

There are tens of millions of AstraZeneca doses stockpiled in the US and the company believes it will have roughly 50 million Covid-19 vaccine doses available to the US government by the end of April. None of those doses are available to Americans now because AstraZeneca has not applied to the Food and Drug Administration for an emergency use authorization, and the vaccine is still going through clinical trials in the US.

AstraZeneca has been approved for use in both Canada and Mexico, and the company itself has asked the Biden administration to consider requests to donate inventory to other nations.

Mexican President Andres Manuel Lopez Obrador announced Monday that he was close to reaching two agreements on vaccines, but he didn't specify which countries would be sending them. Another top official in Mexico publicly asked the US to share AstraZeneca vaccines earlier this week.

A Canadian Embassy spokesperson said that there have been "great engagements" with the Biden administration about Covid-19 and added that "conversations are ongoing" when it comes to getting more Canadians vaccinated. The spokesperson did not comment on the possible swap agreement.

Tensions over vaccine diplomacy

These conversations come as political leaders in both Mexico and Canada are under increasing pressure to secure vaccines amid a wider global scramble for doses.

The US is now ahead of almost every other country in the world when it comes to vaccinating its population and having secured contracts with vaccine producers. Biden said last week that by May 1 all adults will be able to receive vaccines.

The US has contributed $2 billion in total to a global coronavirus vaccine initiative called COVAX, and has pledged to release an additional $2 billion "as we work with other donors to elevate pledge commitments." It has established bilateral agreements with certain countries for vaccine storage efforts, and is working alongside the allies in the Asia-Pacific region to increase production in India.

The Biden administration will eventually share excess vaccines -- beyond the AstraZeneca doses -- and does not see joint efforts alongside US allies as precluding them from unilaterally donating vaccines to other countries down the road, according to the senior administration official.

"We are giving $4 billion to COVAX. But we also know once we get our own country vaccinated, since we have suffered worse than virtually any country besides Brazil -- we are both way up there with over 530,000 deaths -- then we will make any surplus vaccine available to the countries who have not the resources to be able to make it themselves," Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told a hearing of the
House Energy and Commerce Committee on Wednesday.

Biden made the same commitment last week.

"If we have a surplus, we're going to share it with the rest of the world," Biden said. "We're going to start off making sure Americans are taken care of first."

Secretary of State Antony Blinken also said last week that "until everyone in the world is vaccinated, then no one is really fully safe."

The Biden administration's decision to focus inward on vaccines, particularly given the dire need globally and the administration's top priority to re-assert US global leadership, is putting the Biden administration in a somewhat awkward position in comparison to a global rivals.

China has taken a different approach to the US and is exporting vaccines widely before making vaccines widely available at home. Russia and India are also sharing vaccines but not on the same scale as Beijing. The Chinese Foreign Ministry announced March 3 that it is providing free vaccines to 69 countries and commercially exporting them to 28 more.

Some US allies and partners are worried that China's global effort to ramp up vaccine exports and vaccine production agreements so quickly will make it hard for the US to catch up, diplomats told CNN.

Mexico has received AstraZeneca shots from India and is also the focus of China's vaccine diplomacy. Mexican media reported March 9 that the country will receive 22 million doses of China's Sinovac and Sinopharm vaccines.

Beijing's push to aggressively export vaccines has been characterized by US officials as an attempt to spread China's influence and soft power.

When asked on Wednesday if the US will be able to surpass China's efforts on vaccine diplomacy after fulfilling the commitment of vaccinating Americans, Deputy State Department Spokesperson Jalina Porter did not answer the question.

A State Department spokesperson said that while Biden has made the priority to vaccinate Americans clear he is also "deeply focused on the issue of expanding global vaccination, manufacturing, and delivery, which will all be critical to end the pandemic."