President Joe Biden said on Friday he was not confident the US election in November would be peaceful, citing incendiary comments by Republican contender Donald Trump, who still rejects his 2020 defeat.

Trump, who survived an assassination bid in July and another apparent plot in September, alleged widespread fraud after his defeat to Biden in 2020, and pro-Trump rioters riled up by his claims ransacked the Capitol.

"I'm confident it will be free and fair. I don't know whether it will be peaceful," Biden told reporters as he made the first appearance of his presidency in the White House briefing room.

"The things that Trump has said and the things that he said last time out when he didn't like the outcome of the election were very dangerous."

Meanwhile, at the same press briefing, Biden advised Israel against striking Iran's oil facilities, saying he was trying to rally the world to avoid the escalating prospect of all-out war in the Middle East.

Biden added that Israel's Benjamin Netanyahu "should remember" US support for Israel when deciding on next steps.

"If I were in their shoes, I'd be thinking about other alternatives than striking oil fields," Biden told reporters, when asked about his comments a day earlier that Washington was discussing the possibility of such strikes with its ally.

Biden added that the Israelis "have not concluded how they're what they're going to do" in retaliation for a huge ballistic missile attack by Iran on Israel on Tuesday. (AFP)