Hacked emails published by Wikileaks appear to show Qatar pledging to donate $US1 million ($A1.3 million) to Hillary Clinton's family's charitable foundation, despite her promise to curb new donations by foreign governments while US secretary of state.

In an email from 2012, a senior official from the Bill, Hillary & Chelsea Clinton Foundation informs colleagues that a planned donation by Qatar's government to mark Bill Clinton's birthday came up in a meeting he had with the Gulf state's ambassador.

The ambassador said that he asked "to see WJC 'for five minutes' in NYC, to present $1 million check that Qatar promised for WJC's birthday in 2011," Amitabh Desai, the foundation official, writes in his email, using the former US president's initials.

Hillary Clinton, who is the Democratic nominee for the November 8 presidential election, served as secretary of state from 2009 until 2013.

The hacked email is among thousands published over the last week by the pro-transparency group Wikileaks from the account of John Podesta, the chairman of Hillary Clinton's 2016 presidential campaign.

Clinton's campaign has been embarrassed by this and similar recent hacking attacks on other Democratic Party officials, some of which appear to show Clinton and her aides saying things in private that contradict their public positions. Her spokespeople have not disputed the authenticity of the hacked emails.

The emails released by Wikileaks do not appear to confirm whether Qatar gave the promised $US1 million, although the foundation's website lists the State of Qatar as having given at least that amount. There is no date listed for the donation. A spokesman for the foundation declined to confirm the donation.

Reuters could not rule out the possibility the $US1 million was intended as a birthday present for Clinton personally, not for the foundation. His spokesman did not respond to questions.

Hillary Clinton promised the US government that while she served as secretary of state the foundation would not accept new funding from foreign governments without seeking clearance from the State Department's ethics office.

The agreement was designed to dispel concerns that US foreign policy could be swayed by donations to the foundation. Clinton's Republican rival in the presidential election, Donald Trump, has seized on the foundation, calling it a front for corruption. Clinton's campaign dismisses this as a political smear.

The State Department has said it cannot cite any instances of its ethics officials reviewing or approving new donations from foreign governments to the foundation while Clinton served as the country's top diplomat from 2009 until 2013.