US President-elect Donald Trump has appointed his son-in-law Jared Kushner to serve as his senior adviser in the White House, raising concerns about conflict of interest and nepotism.

Trump said in a statement on Monday that he is "proud to have him in a key leadership role in my administration.

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

Kushner, a New York real estate businessman and investor, will join Chief of Staff Reince Priebus and Chief Strategist Steve Bannon in implementing Trump's domestic and foreign policies.

WATCH: Trump vs America - Presidential conflict of interest?

Kushner is married to Trump's daughter, Ivanka.

He may not even be eligible for the post under a 1967 law that bars government officials from hiring relatives, though whether the regulation applies to cabinet posts is not clear.

Kushner's lawyer said the appointment is based on legal judgment that anti-nepotism statute does not apply to the White House.

A senior Trump transition official also said that Kushner will recuse himself from participating in matters that could have a direct effect on his remaining financial interests.

The statement announcing Kushner's appointment adds that he will not receive a salary while in the Trump administration, further diminishing the likelihood that the appointment would run afoul of the anti-nepotism law.

Ethics questions

Al Jazeera political analyst Bill Schneider said it is "not very clear" if the law applies to Kushner's appointment.

"The law itself is very clear. It says that you cannot appointment a relative to a federal agency that you head. But the White House is not a federal agency under the law.

"There can be ethics questions. There can be conflict of interest questions, because Mr Kushner has very widespread international business dealings, including a lot of Chinese investors with companies that he has run. But he is in a process of divesting himself in a lot of those business interests."

Conflict of interest laws also do not apply to the president of the United States, Schneider said.

Kushner played a key role in Trump's campaign and has continued to be one of the most influential figures in the transition team.

Before his involvement in politics, Kushner led his family's real estate company and was publisher of the New York Observer.

He will resign from both posts before entering the administration.

The appointment of relatives to White House posts is not unprecedented. Before the anti-nepotism law was passed, President John F. Kennedy appointed his brother Robert Kennedy to serve as the US attorney general.