US President-elect Donald Trump's son-in-law Jared Kushner will become a senior White House adviser and work on the Middle East and trade deals, transition officials say, in a rare case of a close presidential family member taking on a major job.

Key points: Jared Kushner is married to Donald Trump's daughter, Ivanka

Jared Kushner is married to Donald Trump's daughter, Ivanka Mr Kushner expected to focus on trade policy and the Middle East

Mr Kushner expected to focus on trade policy and the Middle East Anti-nepotism law does not apply to purely White House roles

Mr Kushner, 35, who is married to Mr Trump's daughter Ivanka, is taking the job after receiving legal counsel he would not be violating a US anti-nepotism law, based on court rulings the statute does not apply to the White House.

The position does not require US Senate confirmation.

Mr Trump said in a statement the real estate developer was a "tremendous asset and trusted adviser" during the election campaign and transition.

"He will be an invaluable member of my team as I set and execute an ambitious agenda, putting the American people first," he said.

Ms Trump, who like her husband has been a trusted adviser to the President-elect, will not take on a role in her father's White House but will focus instead on settling her family in Washington.

Both Mr Kushner and Ms Trump will undertake significant divestments of "substantial assets" as they prepare for their move to Washington from New York and face inevitable questions about a potential conflict of interest.

The statement said Mr Kushner would forego his salary while serving in the administration.

"It is an honour to serve our country. I am energised by the shared passion of the President-elect and the American people and I am humbled by the opportunity to join this very talented team," he said.

In a telephone conference with a small group of reporters, lawyers and transition officials said Mr Kushner would work closely with incoming White House chief of staff, Reince Priebus, and senior strategist Steve Bannon in advising the new president.

The officials said he would focus at least in the beginning on trade policy and the Middle East.

Questions remain over legality of appointment

The incoming president has vowed to rewrite international trade deals to make them more favourable to the US and has adopted a pro-Israel stance with a pledge to move the US embassy in Israel to Jerusalem from Tel Aviv.

Sorry, this video has expired Dr Carl Rhodes discusses the legality of Jared Kushner's appointment.

Jamie Gorelick, a New York lawyer who served as deputy attorney-general for former Democratic president Bill Clinton, helped advise Mr Kushner on whether he would violate a 1967 anti-nepotism statute and said he would not.

"I'm not saying that there isn't an argument on the other side, and I respect the people who have made the argument on the other side. I just think we have the better argument," she said.

Ms Gorelick said Congress in 1978 authorised the president to hire personnel for the White House office "without regard" to federal personnel laws like the anti-nepotism statute and the Justice Department had described that authority as unfettered and sweeping.

"Even without that law, two DC Circuit decisions strongly suggest that the White House Office is not an 'agency' under the anti-nepotism statute, a position supported by the views of the Justice Department under presidents Bill Clinton and George W Bush," Mr Gorelick said.

Reuters