A memorial dedicated to slaves and African-American workers at the University of North Carolina at Chapel Hill was vandalised on Sunday, the university said, as the institution is still reeling from tensions over a Confederate monument that was toppled by protesters last year.

The memorial, called the Unsung Founders Memorial, was vandalised by two people, including one person with ties to a group called Heirs to the Confederacy, the university said.

The Unsung Founders Memorial was installed in 2005 to honour “those men and women of colour — enslaved and free — who helped build the Carolina we all know and love,” according to the university.

It features a stone tabletop six feet in diameter that is held up by 300 bronze figurines.

At about 1:30am on Sunday, the memorial was defaced with urine and racist language written in permanent marker, university police said.

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“These events challenge not only our most fundamental community values, but also the safety of our campus,” Kevin M. Guskiewicz, the campus’ interim chancellor, said in a statement Sunday.

The vandalism comes more than six months after the toppling of a 105-year-old Confederate statue called “Silent Sam,” which prompted heated protests and drew national attention to the university.

Many asserted that the statue was an emblem of white supremacy.

Students had protested the statue for decades, but it was toppled amid a greater reckoning nationwide over what to do with Confederate symbols and tributes.

Confederate monuments have been removed across the country, from Los Angeles to Brooklyn.

Heirs to the Confederacy had previously organised events in support of the statue. Lance Spivey, chairman of the group, said Monday that he was looking into the university’s allegations about the vandalism of the Unsung Founders Memorial.

He said at least two members of the group, whom he did not name, were on the campus Saturday night, but he did not have any information to suggest that they defaced the memorial. If they did vandalise it, he said they did so in a “renegade capacity”.

He said he believed that the two members were cooperating with the police, and that if the allegations against them were proved true, the group would also take “whatever punitive measures it deems necessary”.

The Silent Sam statue, which was located near the Unsung Founders Memorial, depicted a Confederate soldier grasping a rifle. The soldier is considered “silent” because he has no ammunition for his weapon.

Harry L. Smith Jr., chairman of the university’s board of governors, which is elected by the state legislature, had previously called the toppling of Silent Sam an act of vandalism.

After the statue was toppled, what remained was a tall base with a relief that depicted a woman beseeching a university student to join the Confederate Army.

In January, the board voted to expedite the resignation of the school’s previous chancellor, Carol L. Folt, after she authorised the removal of the base of the statute. She had previously said she would stay on through the end of the academic year.

A spokeswoman for the university said Monday that the board was expected to decide what to do with the statue and its base in May. Until then, they are being stored at a secure, undisclosed location on campus, she said.

The Unsung Founders Memorial, created by artist Do-Ho Suh, was dedicated in November 2005.

“What we do today will not rectify what our ancestors did in the past,” the university’s then-chancellor, James Moeser, said at a ceremony that year.

“But this memorial, I believe, attests to our commitment to shed light on the darker corners of our history.

“Yes, the university’s first leaders were slaveholders. It is also true that the contributions of African-American servants and slaves were crucial to its success.”

The university said it was not aware of any previous times the memorial had been vandalised.

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The university police said Monday that an art installation on campus was also vandalised with racial slurs. The individual with ties to the Confederate group was identified on surveillance footage, the university said.

The police declined to name the individuals they were seeking, but a spokesman said they had warrants out for their arrests.

The police also declined to be more specific about what was written on the memorial or provide more information about the Heirs to the Confederacy group and the connection to the vandalism. They said an investigation was continuing.

The Unsung Founders Memorial has been cleaned by the university, which has placed barricades around the memorial to “deter future incidents,” the police said.