Hillary Clinton has released her tax returns, adding to the pressure on her Republican rival for the White House, Donald Trump, to do the same.

 The Democratic presidential candidate paid an effective federal tax rate of 34.2% last year.

Her running mate Tim Kaine, along with his wife Anne Holton, paid a rate of 20.3%, his returns show.

Trump, a hotel developer with a fortune estimated to be in the billions, has refused to release his.

Presidential candidates typically release their tax returns to the media to show their effective tax rate, charitable donations and other financial details.

Trump, who has released a self-reported financial disclosure form, said he will not make his tax returns public until the Internal Revenue Service completes audits of them.

 What's in Donald Trump's tax returns?

The IRS has said Trump is free to release his returns. Trump would be the first presidential candidate in decades not to release his returns.

 Then-President Richard Nixon released his tax returns in 1973, starting an informal precedent.

In 2012, then-Republican presidential Mitt Romney reluctantly released his returns.

The returns became a campaign issue after the documents showed he paid an effective tax rate of 14.1%, much lower than the typical rate for top earners.

"Hillary Clinton and Tim Kaine continue to set the standard for financial transparency," said a Clinton campaign spokeswoman, who called on Trump to do the same.

Hillary Clinton's return was filed jointly with her husband former President Bill Clinton. The couple earned more than $10m in 2015, the documents say.

Most of the income came from Clinton's speaking fees as Hillary Clinton has been campaigning for president. Hillary Clinton earned about $3m from book royalties.

The Clintons have disclosed tax returns for every year since 1977.