The company also said it had shared with the federal government “every aspect” of its production and distribution process. “They have visited our facilities, walked the production lines and been updated on our production planning as information has become available,” the statement said.

This fall, Pfizer halved initial estimates that it could make 100 million doses by the end of the year after running into manufacturing delays caused by difficulties locating equipment and raw materials, as well as needing more doses for an expansion of its clinical trial. In November, the chief executive, Dr. Albert Bourla, said about 25 million doses would go to the United States. On Wednesday, a Pfizer spokeswoman said that the company would be able to distribute 20 million doses in December in the United States.

The controversy over short-term deliveries is playing out against a backdrop of tense negotiations between Pfizer and the federal government over a new contract for tens of millions of more doses in the first half of next year. The two sides hope to reach an agreement by Christmas, but Pfizer has said it needs the federal government to use its authority to force suppliers to prioritize its orders — a request that one person familiar with the negotiations said has been pending for months.

The government wants Pfizer to sell it 100 million more doses — enough to cover an additional 50 million Americans — between the start of April and the end of June. Pfizer has said that it can only provide about 70 million doses then because other countries have already bought its remaining stock.

The issue is especially fraught because, according to people familiar with Pfizer’s version of events, the firm repeatedly asked the Trump administration to pre-order more doses beginning in late summer but the administration failed to act until Nov. 25 — more than two weeks after Pfizer announced the results from clinical trials showing its vaccine was safe and more than 95 percent effective.

Now both sides are scrambling to figure out how Pfizer can boost its manufacturing to double the number of doses the firm can deliver for Americans in the first half of next year. So far, the Trump administration has only locked in a total of 300 million doses from Pfizer and Moderna. Because both vaccines require two doses, excluding the children and teenagers for whom no vaccine is yet approved, that still leaves more than 100 million Americans uncovered.

Alex M. Azar, the secretary of Health and Human Services, alluded to the friction with Pfizer in an interview on Thursday morning with CNBC, saying “I do wish we would just stop talking about this Pfizer thing.” He added that the federal government was willing to help Pfizer manufacture more “if they are willing to take our help.”

Abby Goodnough contributed reporting.