China warned its students studying in the U.S. to be vigilant as the Trump administration steps up restrictions on academic visas amid growing trade tensions between the two countries.

“For some time, some of the visas for Chinese students studying in the United States have been restricted, with the review period extended, the period of validity shortened and the refusal rate increased,” the Education Ministry said in a statement published Monday by the official Xinhua News Agency.

“The Ministry of Education reminds students and scholars to strengthen risk assessments before studying abroad, enhance their awareness of prevention and make appropriate preparations,” it said.

U.S. worries about technology and intellectual property theft by China have been at the center of the deepening trade war between the two sides, and President Donald Trump’s administration has increased scrutiny of foreign students and researchers.

American universities remain open to cooperation and welcome Chinese students despite the current trade tensions, state broadcaster China Central Television said, citing Education Ministry spokeswoman Xu Mei. The number of students studying in the U.S. was stable, it cited Xu as saying.

Earlier: China Backs Yale Stance on Foreign Students, Rips U.S. Actions

Yale University President Peter Salovey pledged support for international students in an open letter late last month, reaffirming the Ivy League school’s commitment to its foreign talent.

Salovey’s missive came days after Emory University said it terminated two Chinese-American professors of human genetics, Li Xiao-Jiang and his wife Li Shihua, for failing to disclose research funding from China and their work for Chinese universities while receiving federal grants.

— With assistance by Dandan Li, and Li Liu