A former top United Nations official and a billionaire real estate developer from the Chinese territory of Macau were accused on Tuesday of engaging in a broad corruption scheme, according to federal prosecutors in Manhattan.

The former president of the United Nations General Assembly, John W. Ashe, a diplomat from Antigua, was one of six people identified in a criminal complaint outlining a bribery scheme that involved more than $1 million in payments from sources in China for assistance in real estate deals and other business interests.

The case is highly embarrassing to the United Nations, which had vowed to act with greater transparency and accountability after past scandals. Mr. Ashe is the most senior diplomat to be accused of such graft, and it remains unclear whether the case will prompt the organization to review how it elects leaders of the General Assembly. It is different from the oil-for-food program scandal in Iraq a decade ago, when an independent commission found widespread abuse.

Secretary General Ban Ki-moon said through his spokesman that he was “shocked and deeply saddened” at the accusations of corruption.