Robert F. Kennedy Jr, scion of a famous American Democratic political family, announced an independent bid for president of the United States on Monday in Philadelphia.

Kennedy, 69, an environmental lawyer who has been critical of vaccine policy, the pharmaceutical industry and US health agencies, could play a potential spoiler role in the 2024 election.

President Joe Biden and former president Donald Trump are so far considered to be the leading Democratic and Republican candidates next year. Kennedy's announcement was criticized by members of both parties, as well as by members of his immediate family.

Kennedy said Biden and Trump are "both right" about his potential spoiler role. "My intention is to spoil it for both of them," he said.

"I've come here today to declare our independence from the tyranny of corruption, which robs us of affordable lives, our belief in the future, and our respect for each other," Kennedy said Monday in a 48-minute speech.

"But to do that, I must first declare my own independence — independence from the Democratic Party and from all other political parties," said Kennedy, whose father, Senator Robert F. Kennedy, and uncle, President John F. Kennedy, were felled by assassins' bullets in the 1960s.

"I haven't made this decision lightly. It's very painful for me to let go as a party of my uncles, my father, my grandfather and both of my great-grandfathers," he said.

Kennedy has said that he has not been treated fairly in the Democratic primary process.

"Biden and the party pushed to change the first primary state from New Hampshire — where Mr Kennedy, who has New England roots, enjoys a base of support — to South Carolina, the state that rescued Mr Biden's primary campaign in 2020," The New York Times wrote.

The Democratic National Committee also has not scheduled any debates that would give Kennedy a chance to reach a wider audience.

Kennedy also criticized powerful segments of American society.

"We declare independence from the corporations that have hijacked our government. We declare independence from Wall Street, from Big Tech, from Big Pharma, from Big Ag, from the military contractors and their lobbyists," he said.

"How can we guard life when the for-profit corporations have captured the public agencies that are supposed to protect us?

"We declare independence from the mercenary media that is here to fortify all of the corporate orthodoxies from their advertisers that urge us to hate our neighbors and to fear our friends," Kennedy said.

During Kennedy's speech, four of his siblings released a statement saying their brother's campaign would be "dangerous to the country".

"Bobby might share the same name as our father, but he does not share the same values, vision or judgment," said Rory Kennedy, Kerry Kennedy, Kathleen Kennedy Townsend and former congressman Joseph P. Kennedy II.

The Republican National Committee, which sent an email on Monday titled "23 Reasons to Oppose RFK Jr", called Kennedy "just another far-left Democrat" who endorsed Hillary Clinton and wants to end the oil-extraction method of fracking.

A Democratic National Committee spokesman, asked for comment by Time.com, responded with an eye roll emoji.