At the same time Cheryl Mills was working as Hillary Clinton's chief of staff during the Democratic presidential candidate's tenure as secretary of state, she was also employed part time for New York University as she helped the school negotiate with officials in Abu Dhabi to build a campus in the Persian Gulf city, Mills told The Washington Post in an interview released Monday.

Mills worked at the State Department as an unpaid "temporary expert-consultant," a status "that allowed her to continue to collect outside income while serving as chief of staff," the Post said.

NYU paid Mills $198,000 in 2009, which is when she held the two positions simultaneously for four months as she helped NYU set up a new campus in the United Arab Emirates. She then collected an additional $330,000 in vacation and severance packages when she left NYU later that year, according to the Post.

Mills said she worked "very hard" to abide by State Department conflict of interest rules, but the new revelations are likely to raise additional questions about Clinton allowing her top aides to split their time between official government work and work benefiting private interests.

Another top Clinton aide, Huma Abedin, worked as Clinton's deputy chief of staff in 2012 while simultaneously being employed by the Clinton Foundation, the family's charity, and at a consulting company with close ties to the Clintons. Mills was also on the foundation's unpaid board for a brief period after being brought on at the State Department.

"I try to understand the rules and follow them. And I try to make sure that I'm disclosing my obligations," Mills told the Post. "I don't know if I'm ever perfect. But I was obviously trying very hard to make sure I was following those rules and guidelines."

Paul C. Light, an NYU professor who has studied government employment in depth for decades and previously served as the head of the Center for Public Service at the Brookings Institution, told the Post that the arrangement "is exceedingly unusual, perhaps exceptional in the history of modern federal bureaucratic leadership."

"I'm amazed that anyone would take on such a wide-ranging agenda and live to tell about it, especially given the competing demands on her time and the sharp boundaries between the worlds she had to navigate," he added.

Richard W. Painter, an NYU law professor who worked as a White House ethics lawyer under President George W. Bush, called the arrangement "problematic" but said said Mills' work "probably complied with the law, provided she did no work at the State Department that would financially affect NYU and its overseas campus," according to the Post. "At this level, that you would make someone a GS-15 and yet have them continue to be a lawyer for a large academic institution or a large law firm - that I've never seen," he said.

"At this level, that you would make someone a GS-15 and yet have them continue to be a lawyer for a large academic institution or a large law firm - that I've never seen."