A secret $1bn US property empire amassed by members of the Saudi royal family is the subject of a bitter legal dispute that threatens to reveal the extent of the family's American business interests.

The oil giant BP and the British defence contractor BAE Systems are among the tenants of companies associated with Prince Abdul Aziz bin Fahd, the playboy son of the late King Fahd, according to court documents.

Lawyers for the companies are asking a judge to keep their ultimate ownership secret, but correspondence between the two sides currently remains on the record in a New York courthouse.

The documents reveal that over the past 15 years, Prince Abdul Aziz and a relative, Sheikh Khalid N Al Assaf, amassed a property portfolio that spans the US, from BAE offices in Reston, Virginia, near the capital Washington, to the headquarters of the television company Starz in California. They also purchased two of the four buildings in the office complex that BP uses as its US headquarters in Houston, Texas.

In an affidavit provided to the court by David Hill, a Texan real estate executive who says he helped manage the portfolio, it is claimed that the royal family held ownership of the properties through a complex network of foreign and US companies. Since 1996, Prince Abdul Aziz and his co-owners made a profit of $379m buying and selling properties in the US and they still own 15 complexes across nine states, for which they paid $978m, Mr Hill says.

The prince met his US property managers repeatedly * Los Angeles, the Bahamas, Cancun in Mexico, and at the Al-Yamamah royal palace in the Saudi capital Riyadh, according to the affidavit.

Prince Abdul Aziz is the youngest son of King Fahd, with a personal fortune estimated in the billions of dollars. He has few governmental responsibilities of his own, and his international playboy lifestyle was on show in another New York court earlier this year when one of his entourage was convicted of raping a woman at the swanky Plaza hotel, where the prince had rented more than 50 rooms.

The claims about the Saudi royal family's extensive US property holdings have come to light in a case in New York Supreme Court involving Mr Hill and a business partner, Howard Hallengren. The two men and the firms they worked for mismanaged the portfolio and took unapproved fees, it is claimed. The pair say the claims are untrue and are petitioning the court to prevent themselves being dragged into arbitration.

One of the claims is that their firm took illegal payments running into hundreds of thousands of dollars when BP negotiated with them to extend its lease in Texas in a new five-year deal worth $49m.

Lawyers for the portfolio companies, meanwhile, are fighting to keep the prince's identity secret. Naming the "ultimate and beneficial owners" is irrelevant because the case involves only US-incorporated entities, attorney Justin Garbaccio wrote to the judge, and Mr Hill and Mr Hallengren have named them "solely to harass and/or embarrass those parties... When faced with the instant application to seal [the names], petitioners took the opportunity in their response to repeatedly and gratuitously name said 'owners' as often as possible."