The ruling upends a principle known as affirmative action which has been in place since the 1960s as a measure designed to increase diversity in the American college system.

The nine justices of the US Supreme Court had been considering two cases concerning admissions at Harvard and at the University of North Carolina (UNC).

They ruled 6-2 against Harvard and 6-3 against UNC, siding with the Students for Fair Admissions group which brought the cases.

The group successfully argued that the universities race-conscious admissions policy violated the 1964 Civil Rights Act which bars discrimination based on race, colour or national origin.

In a written summary of the historic decision, Chief Justice John Roberts said: "Many universities have for too long wrongly concluded that the touchstone of an individual's identity is not challenges bested, skills built, or lessons learned, but the colour of their skin."

While acknowledging that the university policies were "well-intentioned", he wrote: "Harvard's admissions process rests on the pernicious stereotype that 'a black student can usually bring something that a white person cannot offer.'"

The Supreme Court ruling is as controversial for liberal America as the policy it overturns is for conservative America.

Opinion polls suggest the nation is divided but with a majority disagreeing with the Supreme Court decision.

In the context of university admissions, affirmative action was a policy designed to increase diversity in America's educational institutions and the employment sector into which they feed.

As a form of positive discrimination, it is deeply controversial.

Supporters say that by considering race as a factor in the admissions process, but not the determining factor, diversity has increased.

Opponents point to the 14th amendment of the US Constitution which requires that all races be treated equally.

The Supreme Court argued that racial classifications must be removed.

In a signal of the importance of the decision, the impact it will have and the politicisation of the ruling, President Biden made a televised statement giving his reaction.

'Colleges are stronger when racially diverse'

The president said: "For 45 years the United States Supreme Court has recognised the colleges' freedom to decide how to build diverse student bodies with the responsibility of opening doors of opportunity for every single American…"

He continued: "I believe colleges are stronger when racially diverse, [the] nation is stronger because we're tapping into [its] full range of talent.

"While talent, creativity and hard work are everywhere, equal opportunity is not everywhere... [we] cannot let this decision be the last word."

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Seeking to clarify what he believes are misinterpretations of affirmative action, he said: "Many people wrongly believe that affirmative action allows unqualified students to be admitted ahead of qualified students.

"This is not how college admissions work. Rather, colleges set out standards for admission.

"And every student, every student, has to meet those standards, then and only then, after first meeting the qualifications required by the school, do colleges look at other factors, in addition to their grades, such as race."

President Biden pointed to research from the National Bureau for Economic Research carried out in 2017 which concluded that a student from the top 1% of family income in America is 77 times more likely to get into an elite Ivy League college than one from the bottom 20% of family income.

More than 96% of the top 1% in America are white.

Trump praises historic ruling

Former President Trump, whose appointment of three conservative Supreme Court Justices pushed the court to the right, praised the decision.

In a statement, Karoline Leavitt, spokeswoman for Make America Great Again Inc, said: "President Donald Trump made today's historic decision to end the racist college admissions process possible because he delivered on his promise to appoint constitutionalist justices.

"America is a better nation as a result of the historic rulings led by Donald Trump's three Supreme Court nominees."

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Harvard criticises decision

Reacting to the ruling, Harvard University President Lawrence S. Bacow said: "For almost a decade, Harvard has vigorously defended an admissions system that, as two federal courts ruled, fully complied with longstanding precedent.

"In the weeks and months ahead, drawing on the talent and expertise of our Harvard community, we will determine how to preserve, consistent with the Court's new precedent, our essential values."

A number of US States already have state-level bans on race-based admissions in place.

They include Arizona, California, Florida, Georgia, Oklahoma, New Hampshire, Michigan, Nebraska and Washington.