PHOENIX – Nine Chinese students who were returning to the U.S. as undergraduate students at Arizona State University were detained at Los Angeles International Airport, university officials said.

The students were detained by Customs and Border Protection officials "over the last week," the university said in a statement Friday. The students were "denied admission to the U.S. to continue their studies" and were sent back to China, ASU said.

"We are working as quickly as possible to coordinate with the federal government to understand the circumstances surrounding these actions and to rectify the situation," ASU said.

ASU said it has not been able to get answers on why the students were detained and sent back. When contacted by The Arizona Republic, customs officials responded that it was after regular business hours, so they couldn't immediately comment.

Despite returning to China, they're still enrolled at ASU, working through ASU Online, an ASU official said. The university expects some of the detained students to graduate this semester, the official said.

College costs:For undocumented Arizona high school grad, Yale is more affordable than ASU

The detentions come amid an increasingly tense relationship between the U.S. and China. But problems for international students aren't just affecting Chinese students at U.S. universities.

News outlets have reported delays and problems with visas for international students from other countries under the Trump administration. The New York Times reported students from various countries were facing issues with visas.

Earlier this week, the Harvard Crimson reported a Palestinian student was detained by Customs and Border Protection and sent home to Lebanon. In that instance, the student claims customs officials found posts from people that included political views that opposed the U.S. on his friends' list.

The posts were not from the student himself, the student told the Crimson.

ASU also had to close its Confucius Institute, which was funded by the Chinese government, to continue receiving funds from the Department of Defense for a language program.

Students' electronics were searched

The university said in a statement Friday that the detentions weren't based on academic dishonesty issues, despite a media report to the contrary. Customs officials haven't told ASU it was related to academic dishonesty, the university said.

"In fact CBP has given ASU no information on what has transpired," the university said.

If there were an academic dishonesty issue, that's the purview of ASU, not customs officials, ASU said.

"All of the students caught in this situation were academically eligible to return to ASU and to the United States under their visas," ASU said.

The detention happened as students were returning to the country for the fall semester.

Since then, ASU has reached out to "all levels of federal government," the university said. ASU President Michael Crow sent letters to Secretary of State Michael Pompeo and acting Secretary of Homeland Security Kevin McAleenan.

"In each case, the students were in possession of all needed documentation to enter the U.S. yet they were refused entry at the airport, told they needed to return to China, that they needed to pay for their own airline ticket to do so or face a ban from re-entering the U.S. for five years," Crow wrote to the federal officials.

Crow wants a review of the individual situations for the nine students and a review of the procedures that now include searching electronic devices carried by students who enter the U.S.

"In our country, where we value due process and celebrate the different ways in which our government behaves from that of the arbitrary and capricious behavior of other nations, it is beyond my comprehension how the U.S. government could establish and implement policies that bring about the outcomes we are now witnessing," Crow wrote.

In a statement issued earlier Friday to ABC15, Customs and Border Protection noted there are many categories that applicants for admission to the country have to meet in order to enter.

"The Chinese students were deemed inadmissible to the United States based on information discovered during the CBP inspection," the CBP statement said.

Follow Rachel Leingang on Twitter: @rachelleingang