A former president of the United Nations General Assembly turned the world body into a "platform for profit" by accepting over $1 million US in bribes from a billionaire Chinese real estate mogul and other businesspeople to pave the way for lucrative investments, a prosecutor alleged Tuesday.

John Ashe, a former UN ambassador from Antigua and Barbuda who served in the largely ceremonial post as head of the 193-nation assembly from September 2013 to September 2014, faces tax fraud charges in what authorities call a conspiracy with five others, including Francis Lorenzo, a deputy UN ambassador from the Dominican Republic who lives in New York.

U.S. attorney Preet Bharara repeatedly noted that it was early in the investigation and told reporters that as it proceeds: "We will be asking: Is bribery business as usual at the UN?"

He added: "I wouldn't be surprised if we see other people charged."

United Nations Bribery Scheme

U.S. attorney Preet Bharara announces an indictment against six individuals during a news conference on Tuesday. (Mark Lennihan/Associated Press)

The prosecutor said Ashe "converted the United Nations into a platform for profit" when bribery opportunities were dangled before him by Chinese billionaire Ng Lap Seng, 67, and others.

"We obviously just learned of the very serious allegations this morning," Stephane Dujarric, spokesman for UN Secretary General Ban Ki-moon, told reporters. Dujarric said Ban was "shocked and deeply troubled" by the allegations that "go to the heart and integrity of the UN."

Still, he challenged Bharara's insinuations, saying, "Corruption is not business as usual at the UN." He said the UN's legal department and senior officials were not informed of the probe in advance.

'Corruption has no place in the United Nations or anywhere else.' - Mogens Lykketoft, UN General Assembly president 

Dujarric noted that the president of the UN General Assembly "does not report to the secretary general and is completely independent in functions."

Antigua and Barbuda Prime Minister Gaston Browne told The Associated Press on Tuesday that the government of the eastern Caribbean state would fully co-operate with U.S. authorities. The previous government employed Ashe.

"This has serious implications for the country. You're talking about an international platform for peace and global security being used for corrupt purposes," Browne said.

Those charged in the criminal complaint unsealed Tuesday in Manhattan federal court included Ng, who was arrested two weeks ago along with his chief assistant, Jeff C. Yin, 29, a U.S. citizen whose bail was revoked last week over allegations he lied to investigators after his arrest.

Ng's attorney, Alex Spiro, said in a statement that his client "committed no crime."

Lawyers for Yin and Lorenzo, 48, did not immediately respond to requests for comment.

'A sterling reputation'

U.S. Magistrate Judge James Francis set bail at $1 million and ordered electronic monitoring for Ashe after rejecting the government's request that he be held without bail as a flight risk. Francis noted that two tax charges carry a total potential maximum penalty of six years in prison.

"He has every incentive to flee," said Assistant U.S. Attorney Daniel Richenthal.

The prosecutor said in court that Ashe made incriminating statements related to the alleged bribery scheme following his arrest and more serious charges were possible.

"It's likely going to get worse for him, and it's certainly not going to get better," he said.

Defence lawyer Robert Van Lierop said the defence team would "assert the full force of immunity" on Ashe's behalf. He also said his client wanted to stay and fight to preserve his good name.

"He enjoys a sterling reputation, not only at the United Nations but internationally," Van Lierop said.

Van Lierop told reporters outside court he expects his client to be vindicated.

A message asking for comment left at Lorenzo's mission was not immediately returned. Lorenzo, Yin and Ng were ordered held without bail.

Diego Rodriguez, head of the FBI's New York office, said the charges should be a warning "to those who come to the United States from other countries with corruption plans or bags full of cash."

According to allegations in court papers, 61-year-old Ashe used his UN positions to support a multibillion-dollar UN-sponsored conference centre that Ng hoped to build as his legacy in Macau, where he lived, and to help Ng meet government officials from Antigua. Prosecutors said the conference centre would function as a sort of satellite operation for the world body.

In a 2012 letter to the UN secretary general about the centre, Ashe promoted Ng's business group by name.

The scheme unfolded over the course of nearly three years, from 2011 through 2014, prosecutors said.

Private jets and luxury cars

Ng and his assistant had been held by federal authorities on charges they lied about plans for $4.5 million in cash brought into the U.S. over several years aboard private jets.

Prosecutors say some bribe money funded first-class airfare for Ashe, his wife and two children to New Orleans, where they stayed in an $850-a-night hotel room.

Other money, they said, was used to lease a luxury car, pay his home mortgage, buy Rolex watches and custom suits, and construct a $30,000 basketball court at his home in Dobbs Ferry, New York, where he was arrested Tuesday. He opened two bank accounts to receive the funds and then underreported his income by more than $1.2 million, officials said.

Mogens Lykketoft, the UN General Assembly's current president, told reporters Tuesday that member states would decide whether to create more transparency for the world body.

"Corruption has no place in the United Nations or anywhere else," he said.

Prosecutors said two other arrested individuals were involved with Ng. They were identified as Sheri Yan, 57, and Heidi Park, 52, both naturalized U.S. citizens who reside in China and helped facilitate the scheme, prosecutors said. Both were ordered held without bail. Their lawyers did not comment outside court.

The United Nations has known for years that the office of the General Assembly president had transparency issues.

A UN internal audit warned in 2010 that some General Assembly presidents had supplemented their office budgets with "direct agreements" with member states and that the presidents were not required to report that money. It gave no details.

"The lack of transparency concerning such funds may pose a reputational risk for the organization," the audit said.