Updated

Clemson University and the NAACP said Tuesday they are investigating an off-campus party held during the Martin Luther King Jr. weekend that offended some black students because their white peers drank malt liquor and at least one student wore black face.

Pictures from the party were posted online, and Clemson officials learned of the Jan. 14 party this past weekend. The school is probing whether students were harassed or whether there was underage drinking.

Click here to see two videos about the incident

Clemson President James Barker wrote in a letter to students and faculty that he was "appalled, angered and disappointed" by the party, which "appeared to mock and disparage African Americans."

"Many people have been offended and deeply hurt," he said.

The party organizers issued an unsigned letter of apology, saying, "We invited all races and types of peoples and never meant any racial harm."

"We want everyone to know how sorry we are, and that we are willing to do anything to make things right," the letter said.

The National Association for the Advancement of Colored People was looking into the party and at least three similar events at other colleges around the country, said state chapter president Lonnie Randolph.

Clemson has roughly 1,100 black students out of more than 17,000 undergraduates, the university's Web site says.