WASHINGTON -- President Donald Trump hinted Monday that the U.S. could approve a coronavirus vaccine in October, ahead of the November election, as Joe Biden demanded transparency from the government as it studies the shots.

"This could've taken two or three years, and instead it's going to be -- going to be done in a very short period of time," Trump said during a news conference in which he criticized Biden for his skepticism that the FDA is operating free of political pressure.

"Could even have it during the month of October," Trump added, calling Biden's doubts "political lies."

Many public health officials and scientists have expressed concerns that the Food and Drug Administration is under pressure from the White House to approve a vaccine before Trump faces reelection on Nov. 3. Americans may be unwilling to receive a shot if they believe it was rushed to market based on the campaign timetable.

"The vaccine will be very safe and very effective," the president said Monday. "And it'll be delivered very soon. Now, you could -- you could have a very big surprise coming up."

Before Trump's news conference, Biden said he would heed the advice of scientists about whether to get a coronavirus vaccine if one were to become available before November's presidential election.

"I'd want to see what the scientists said," he told reporters Monday outside a supporter's home in Lancaster, Pennsylvania.

Asked if he would trust Anthony Fauci and the Food and Drug Administration, Biden redirected, saying he'd "want full transparency on a vaccine."

Biden has previously expressed concern about Trump and political appointees pushing for the premature approval of a vaccine in hopes of boosting his re-election chances. "He's undermining public confidence," Biden said of Trump.

Trump fired back during news conference on Monday.

Biden and his running mate, Kamala Harris, "should immediately apologize for the reckless anti-vaccine rhetoric that they're talking right now, talking about endangering lives, and it undermines science."

Biden said he worries Trump's behavior will damage public confidence if there's an effective vaccine.

"One of the problems with the way he's playing with politics is he's said so many things that aren't true I'm worried if we do have a really good vaccine, people are going to be reluctant to take it," he said.

Biden also said he'd want an effective vaccine no matter the electoral consequences.

"If I could get a vaccine tomorrow I'd do it," he said. "If it cost me the election I'd do it. We need a vaccine and we need it now."

(With assistance by Josh Wingrove.)

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