Image copyright Reuters Image caption US President Donald Trump has accused the Bidens of corruption

The son of US presidential contender Joe Biden is to step down from the board of a Chinese company amid fierce attacks by President Donald Trump.

Hunter Biden would also not work for any foreign-owned companies if his father were elected, his lawyer said.

Mr Trump has called on China and Ukraine to investigate Joe Biden over his son's activities in both countries, without any evidence of any wrongdoing.

The issue is central to an impeachment inquiry against the US president.

Mr Trump and his supporters have accused Joe Biden of abusing his power when he was vice-president to pressure Ukraine to back away from a criminal investigation that could have implicated his son who then worked for a Ukrainian energy company.

Media playback is unsupported on your device Media caption Trump rally's new hate figures - the Bidens

He has also accused Hunter, 49, of using his position of influence to get China to invest in a fund he was involved in.

The impeachment inquiry begun by opposition Democrats in the US House of Representatives centres on allegations that the president broke the law by soliciting help from a foreign power - Ukraine - for electoral gains.

What did Hunter Biden say?

A statement released through Hunter Biden's lawyer said he would resign by 31 October from the board of BHR (Shanghai) Equity Investment Fund Management Company.

It said he joined the board in an unpaid position "based on his interest in seeking ways to bring Chinese capital to international markets".

The statement said Hunter would "readily comply" with guidelines issued by his father if he was elected president "to address purported conflicts of interest, or the appearance of such conflicts", and would, "in any event", agree not to serve on the boards of or work on behalf of foreign-owned companies.

The statement also detailed the nature of his work in Ukraine and China, stressing that there had been no wrongdoing.

Image copyright Getty Images Image caption Hunter Biden (right) walks off Air Force Two with his father during the US vice-president's official trip to US Beijing in December 2013

What is the background to the fund?

Hunter Biden and his daughter Finnegan accompanied Joe Biden on the vice-presidential plane, Air Force Two, for an official trip to Beijing in December 2013.

It later emerged that during the trip, Hunter Biden met Chinese banker Jonathan Li, his eventual partner in the BHR (Shanghai) Equity Investment Fund Management Company.

The Chinese business licence for the new fund was issued by Shanghai authorities 10 days after the Bidens' visit. Hunter Biden was named as a member of the board.

His lawyer, George Mesires, has told US media his client did not acquire an equity interest in the fund until 2017, after his father had left office.

Hunter Biden, the lawyer added, only invested about $420,000 (£335,000) for a 10% stake, which would value the fund's total capitalisation at the time at about $4.2m.

This suggests Hunter Biden earned far less than the $1.5bn Mr Trump has alleged he received from business activities in China.

BHR is a private-equity fund backed by some of China's largest state banks, local government and the national pension fund, according to the Financial Times newspaper.

What else has Trump accused the Bidens of doing?

Mr Trump has also accused the former US vice-president and his son Hunter of corruption in their political and business dealings in Ukraine and China, without offering specific evidence.

When Hunter Biden joined the board of Ukrainian natural gas company Burisma in 2014, questions were raised about a potential conflict of interest for his father.

Ukraine was undergoing a political transition after its pro-Russia president was forced out of office, while the elder Biden was the Obama administration's point man for the Eastern European country.

In 2016, Joe Biden pushed the Ukrainian government to fire its top prosecutor, whose office had been scrutinising the oligarch owner of Burisma.

In a speech last year at a think tank, Joe Biden boasted of having forced the prosecutor out by threatening to withhold a billion-dollar loan guarantee to Ukraine.

Mr Trump and his allies accuse Joe Biden of acting to protect his son. However, other Western officials and major financers of Ukraine's government also wanted the prosecutor dismissed because he was seen as a barrier to anti-corruption efforts.

What is the impeachment inquiry?

A Democratic-led inquiry is trying to establish whether Mr Trump withheld nearly $400m (£327m) in aid to nudge Ukraine's newly elected President Volodymyr Zelensky into launching an inquiry into Joe Biden and his son.

In a phone call on 25 July, Mr Trump asked Mr Zelensky for help on the issue.

Media playback is unsupported on your device Media caption What we know about Biden-Ukraine corruption claims

A whistleblower raised concerns about the phone call, prompting the launch of a formal impeachment investigation last month.

The White House this month sent an eight-page letter to top Democrat and House Speaker Nancy Pelosi, calling the inquiry "constitutionally invalid" and therefore stating that President Trump would not be co-operating.