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Media mogul Rupert Murdoch has apologised for a tweet suggesting President Barack Obama is not a "real black president".

In tweets praising Republican candidate Ben Carson, Mr Murdoch wrote: "What about a real black President who can properly address the racial divide?"

After criticism on Twitter, he later tweeted: "Apologies! No offence meant. Personally find both men charming."

Mr Murdoch, 84, is founder of the global News Corporation empire.

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His company owns Fox News Channel and The New York Post and The Wall Street Journal in the US, and Sky News and The Sun and Times newspapers in the UK, among others.

He is ranked as one of the world's most powerful people.

Mr Murdoch has previously tweeted his admiration for Mr Carson, a 63-year-old retired neurosurgeon who is one of 15 hopefuls vying to become the Republican candidate for the US presidency in 2016.

A few days ago, he tweeted: "Everywhere pundits keep underestimating Ben Carson. But public understand humility as admirable, listen to the multi-faceted strong message."

Previously, he has said of him: "Maybe the one to beat. Irreproachable on background, achievements, character, vision."

He took to Twitter again on Wednesday.

Shortly after, he tweeted again:

President Obama, throughout his presidency, has tended to be cautious about race, leaving others to attach racial meaning to his presidency, the BBC's Nick Bryant in New York has written.

This week's New York magazine quotes members of the African-American community as saying they wish he had done more to tackle racial problems.

Mr Carson caused controversy last month when he said a Muslim should not run for president because Islam was inconsistent with the US constitution.

Democrats and black votes

In early August the National Urban League, a black civil rights organisation, gathered in Florida for its annual conference - and attendees and speakers grappled with the upcoming 2016 election and the role that black voters will play. Some of the talk could prove encouraging for Republicans.

"We are a part, as black voters, of a coalition that we've given everything to and can't ask anything from," Van Jones, an environmental activist, lawyer and former Obama adviser, said during a panel on the presidential race.

"As long as that's our position, we're going to continue to be mistreated within our own party."

Blacks have been supportive of other Democratic priorities, such as immigration reform, the environment and gay rights, but are being ignored on matters that concern their communities, he believes.

"The Obama era of black silence on issues that are important to us is over," Jones said.

Read Anthony Zurcher's article in full