Students wearing red handkerchiefs over their faces blocked the doors to Chancellor Marye Anne Fox's offices for hours, while more students inside chanted "Real pain, real change."
They left the office peacefully at sundown, about the same time that leaders of the university's Black Student Union ended talks with administrators in a nearby conference room over demands that include more boosting the African-American curriculum and campus activities. A university spokesman, Jeff Gattas, said there were no arrests and no property was damaged during the takeover.
The noose found dangling from a light fixture on the seventh floor of Geisel Library on Thursday night was the latest in a string of racially charged incidents in the university community, authorities said Friday. Less than two weeks ago, an off-campus party mocking Black History Month ignited racial tensions.
A University of California statement said a student admitted she and two other people were responsible. The statement did not identify the students or their race or include a motive.
In a news conference Friday afternoon, Fox said the student has been suspended but declined to discuss her motive or other students involved.
"This person admitted her involvement in what we consider to be an abhorrent act," said Fox.
Hundreds of students rallied for several hours outside the university administration building Friday, where speakers denounced the noose as an example of intolerance on a campus where less than 2 percent of students are black.
UC and campus authorities did not indicate whether the students would be charged with a hate crime. Under state law, hanging a noose to terrorize is punishable by up to a year in jail.
"Whatever the intent of the authors of this act, it was a despicable expression of racial hatred, and we are outraged," the UC statement said. "It has no place in civilized society, and it will not be tolerated."
To blacks, a noose recalls the days of widespread racism and lynchings.
"How am I supposed to walk into that building? How am I ever going to be safe there?" said ethnic studies major Cheyenne Stevens, who is black.
Mustafa Shahryar, 21, said he had seen the noose as he left the library.
Shahryar, who is from Afghanistan, told the crowd he grew accustomed to racial slurs while growing up in Southern California but was stunned to see the noose.