Democratic White House candidate Hillary Clinton has released her 2015 tax return that sought to pressure presidential rival Donald Trump to disclose his tax returns.

Clinton and her husband Bill, the former president, reported $10.6m in income for 2015.

They paid $3.6m in federal income tax, according to the document released on Friday, which was posted on her campaign website.

Trump has refused to make his filings public, saying they are under audit by the Internal Revenue Service and he'll release them only once that review is complete.

All major US presidential candidates in modern history have released their returns.

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The bulk of Clintons' income, more than $6m, came from speaking fees for appearances made largely before Hillary Clinton launched her campaign in April 2015.

They gave more than $1,042,000 to charity, with $1m going to the Clinton family foundation. That is the financial vehicle the family uses to give money to museums, schools, churches and other charitable causes. It is not the same organization as the better-known Clinton Foundation.

Clinton's running mate Tim Kaine also released his returns for the past 10 years on Friday.   

"Donald Trump is hiding behind fake excuses and backtracking on his previous promises to release his tax returns," Clinton campaign communications director Jennifer Palmieri said. "What is he trying to hide?"

Rather see emails   

Trump senior communications adviser Jason Miller said in a statement that Americans would rather see deleted emails from Clinton's private server, Clinton Foundation records and transcripts of speeches she gave to Wall Street business people.

"We want to see the records the night of Benghazi that explain why Secretary Clinton didn't send in reinforcements as soon as the attack had begun," he said of the 2012 assault on the US consulate in Libya that killed four Americans, including the ambassador.

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Democrats hint that by not releasing his tax returns, Trump may be trying to hide that he pays little to no tax, makes less money than he claims or gives a negligible amount to charity.

Trump, 70, presented the Federal Election Commission with a mandatory personal financial disclosure form in May and says this is enough.

That document gave only an estimate of Trump's assets, liabilities and income.

Trump has said he is worth more than $10bn, but no one has been able to confirm this independently. Forbes magazine estimates Trump is worth less than half that - $4.5bn.

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He turned a deaf ear to calls from his critics for his tax returns at a campaign rally in Pennsylvania, a key swing state where he is lagging behind Clinton in the polls.  

His sinking poll numbers are worrying some Republicans, but party boss Reince Priebus weighed in Friday to show his support.

Over the course of their careers, the Clintons have published all of their tax returns since 1977.

Source: Agencies