"There's movement" in the talks, he added.
Museum and university officials have declined to comment on the matter.
On Wednesday, the museum issued a news release stating that the show - the first high-profile ticketed exhibition in the museum's history - would open as scheduled in a "modified" format.
That meant more than 100 artifacts and two mummies from western China will not be displayed, the release said, "at the request of Chinese officials."
Since then, speculation about the cause of the problem has mushroomed at the museum and university. On Friday, a university source told The Inquirer that regional authorities in Xinjiang in western China had given their approval for the exhibition's Philadelphia venue, but that Beijing cultural authorities had not.
One source said the matter had been taken up by the U.S. Embassy in Beijing.
Mair would not confirm that the embassy had become involved - although Jon Huntsman, the U.S. ambassador to China, is a Penn graduate.
There had been no hint of problems with the show until this week. The Bowers Museum of Art in Santa Ana, Calif., organized the exhibit and showed it last year without incident. The exhibit then went to Houston, again without incident.
The artifacts had been boxed and shipped to Philadelphia, and the mummies were about to follow a week or two ago when, Penn sources said, Chinese cultural authorities ordered the mummies to remain in Houston and the crates to remain closed at Penn.
Should negotiations succeed, the artifacts presumably could be displayed, and the mummies sent on to Philadelphia.
But the Penn Museum has already begun refunding proceeds of advanced-ticket sales, and city tourism officials have stopped offering hotel packages tied to the show. For now, entrance to the exhibit is free with regular museum admission.
That said, Mair characterized negotiations as "really, really intense and critical" at the moment. He declined to comment further.
Contact culture writer Stephan Salisbury at 215-854-5594 or firstname.lastname@example.org.