By Kevin Liptak and Paul LeBlanc, CNN

(CNN) -- President Donald Trump said Sunday that he believed "political reasons" had slowed down the Food and Drug Administration's approval of emergency use authorization for convalescent plasma but that he "broke the logjam" over the last week.

His remarks amount to tacit confirmation that he applied pressure on the agency ahead of its announcement Sunday issuing emergency use authorization for Covid-19 patients.

"I think there might have been a hold up, but we broke the logjam over the last week to be honest," Trump said at a late afternoon news conference announcing the new authorization.

He said he believed there were officials at the FDA and in the Department of Health and Human Services "that can see things being help up and wouldn't mind so much."

"It's my opinion, very strong opinion, and that's for political reasons," Trump continued, insisting that his focus on treatments for coronavirus -- which has slowed the American economy and caused his poll numbers to sink -- was apolitical.

"This has nothing to do with politics," he said. "This has to do with life and death. So we are being very strong, and we are being very forthright, and we have got some incredible answers, and we're not going to let them be held up because every day is lives."

The President last week had accused some health officials of playing politics regarding an EUA for convalescent plasma. When asked about the FDA not having granted an EUA, Trump said the reason was political.

Earlier Sunday, a source who is close to the White House coronavirus task force told CNN the FDA had reviewed additional data to inform its impending EUA decision.

This official has not personally reviewed the data. They added the FDA is under no obligation to consult anyone outside the agency about its decision.

Convalescent plasma is taken from the blood of people who have recovered from Covid-19. At the end of March, the FDA set up a pathway for scientists to try convalescent plasma with patients and study its impact. It has already been used to treat more than 60,000 Covid-19 patients.

However, like blood, convalescent plasma is in limited supply and must come from donors. And while there are promising signals from some studies, there is not yet randomized clinical trial data on convalescent plasma to treat Covid-19. Some of those trials are underway.

Earlier in the briefing, Trump appeared enthusiastic when asked by a reporter from Fox News whether patients should have access to treatments or vaccines before they reach the end of trials.

"We have all of these great, seemingly great answers that are ready to come out, but because of the process it takes -- can we use some of this early under right to try?" he asked, referring to legislation that allows patients access to drugs that are still in the investigation phase.

FDA Commissioner Stephen Hahn declined to answer on Sunday when asked by CNN as the briefing concluded whether there was pressure on him to approve EUA for convalescent plasma.

A prominent vaccine expert told CNN's Wolf Blitzer on Sunday that the White House may have bullied the FDA into giving emergency use authorization to using blood plasma.

"I think what's happening here is you're seeing bullying, at least at the highest level of the FDA, and I'm sure that there are people at the FDA right now who are the workers there that are as upset about this as I am," said Dr. Paul Offit, director of the Vaccine Education Center at Children's Hospital of Philadelphia.

Moving things along quickly is fine, Offit said, but it's the FDA's job to hold products to a standard of safety and efficacy. Offit said he worries that the FDA, like other science-based agencies, "get bullied to do what Donald Trump wants them to do, and I think it's a dangerous game he plays."

The potential side effects of convalescent plasma are not known, Offit said. While he said he thinks it is likely that it is generally a safe product, "until something has been shown clearly to work, we shouldn't put it out there."

It makes sense that administering a serum with high levels of neutralizing antibodies to a person who is mildly ill would help, but "the trick is proving that it makes a difference," Offit said.

The data so far have not proved that the plasma makes a difference, Offit said.

The administration has raised the idea of doing a similar thing with vaccines, sources say. On July 30, during broader negotiations over the coronavirus relief legislation inside House Speaker Nancy Pelosi's office, Senate Minority Leader Chuck Schumer asked the White House officials in the room how things were going on the vaccine effort, according to two sources familiar with the meeting.

It was at that point that White House chief of staff Mark Meadows and Treasury Secretary Steve Mnuchin walked through the various pieces of vaccine development, and then suggested that the AstraZeneca effort could be ready by September. As the conversation continued, the White House officials raised the possibility of an emergency use authorization before phase three trials were completed.

At that point, Pelosi interrupted to tell Mnuchin and Meadows there should be no cutting of corners during the vaccine development process.

The Financial Times first reported the details of the July meeting.

Michael Caputo, the assistant secretary for public affairs at the Department of Health and Human Services, on Sunday denied that there was any effort to fast-track vaccine development for political purposes.

"This is not true, don't believe it. Talk of an October surprise vaccine plot is a lurid Resistance fantasy designed to undermine the President's Coronavirus response. And nobody, but nobody, among the career FDA regulators I know will ever stand quietly for political pressure," Caputo said.

Meadows on Monday morning also dismissed concerns that there's political pressure to fast-track a vaccine, reiterating how Operation Warp Speed will produce vaccines in phase three trials.

"Yeah that's not happening. I can tell you, we're going through a standard clinical process like any other drug would happen and then what we're speeding up is the non-testing side of it," he said.

This story has been updated Monday with additional developments.