The official, who was not authorized to speak about the case publicly and spoke on condition of anonymity, said the U.S. accepted India's request to accredit her to the United Nations, which confers broader immunity than what she enjoyed as a consular official. It would be almost unprecedented for the U.S. to deny such a request unless the diplomat was a national security risk.
The United States asked the government of India to waive the immunity, but the Indians refused, the official said.
The United States then "requested her departure" from the country, the official said.
Authorities say Khobragade claimed to pay her Indian maid $4,500 per month but actually gave her far less than the U.S. minimum wage. The indictment said Khobragade had made or multiple false representations to U.S. authorities, or caused them to be made, to obtain a visa for a personal domestic worker. She planned to bring the worker to the United States in September 2012 when she worked at the Consulate General of India in New York, according to the indictment.
Her arrest last month sparked outrage in India after revelations that she was strip-searched and thrown in a cell with other criminal defendants before being released on $250,000 bail.
Khobragade, India's deputy consul general in New York, has maintained her innocence.
In a letter, prosecutors said there was no need for an arraignment because Khobragade had "very recently" been given diplomatic immunity status; they also mistakenly said she'd already left the United States. But Daniel Arshack, a lawyer for Khobragade, said in a statement soon after that his client was home with her children.
A spokesman for prosecutors later clarified that the mix-up came because the State Department advised that she was to have left the country Thursday afternoon.
The charges will remain pending until she can be brought to court to face them, either through a waiver of immunity or her return to the U.S. without immunity status, the letter from the office of U.S. Attorney Preet Bharara said.
"We will alert the court promptly if we learn that the defendant returns to the United States in a non-immune capacity, at which time the government will proceed to prosecute this case and prove the charges in the indictment," the letter said.