Nine students, including six Americans, who attend New York University in Shanghai were detained by Chinese police in two separate incidents on the same night last week, university personnel and U.S. officials told The Washington Post.

Two of the U.S. students were apprehended at a bar, according to a student and university faculty. One of them, a young man, was kicked in the head by authorities and the other, a woman, sustained bruising as police in plainclothes attempted to apprehend her, the student said.

Seven students in a separate group, which included citizens of the United States, Finland, Morocco and Malaysia, were taken into custody from a house where they gathered for a birthday party, said students and university personnel. The students tested negative for drug use and were released between 11 and 16 hours later, they added.

It is unclear whether the students were arrested as part of China’s increasingly aggressive anti-drug enforcement policies or targeted for political reasons amid worsening relations with the United States.

President Biden’s national security adviser, Jake Sullivan, and Secretary of State Antony Blinken are poised to meet their Chinese counterparts for the first time on Thursday for a session that Blinken called an “important opportunity for us to lay out in very frank terms the many concerns we have.”

When asked about the arrests, a State Department spokesman said that “the Chinese legal system can be opaque and enforcement of local laws arbitrary,” and that the country’s judiciary “does not enjoy independence from political influence.”

“We are aware of the detention and subsequent release of a group of U.S. citizens in Shanghai, China. We stand ready to provide all appropriate consular services,” the spokesman said.

A spokeswoman for NYU, June Shih, said the university does not know why Chinese authorities detained everyone at the birthday party. “We believe that the police were focused on a particular individual,” she said.

Shih said the university thinks the students at the bar were “detained as part of a roundup related” to alleged drug activity.

“The students stated that they were confronted by a person in plain clothes; not understanding that this person was a police officer, the students evidently attempted to depart the scene, and have since reported that they sustained some injuries as police sought to detain them,” Shih said.

One of the students said the police used unnecessary force and created confusion and fear by appearing without a badge or uniform.

“The guy was literally bleeding from his head from getting kicked by the police. They had no translator so they had no idea what was going on,” said the student, who spoke on the condition of anonymity to discuss the interaction with law enforcement. “The girl was beat up for running away from two plainclothes cops with no badge. The guy who got kicked in the face was just trying to call NYU Shanghai public safety.”

The two Americans have parents who work for the Defense Department, people familiar with the incident said.

It is not uncommon for Chinese police to show up at private residences while carrying out counternarcotics operations, but appearing in plainclothes is unusual, as is violence in the absence of a significant escalation.

Some of the students and parents complained about a lack of support from school officials during the detention. But Shih said the university did not intervene while the students were in detention because “Chinese law enforcement has previously indicated that it looks askance upon efforts to intervene before the initial phase of their investigations — i.e., the drug tests — are completed.”

NYU opened its research institution in Shanghai in 2012 in conjunction with East China Normal University and the support of the city.

In recent months, Chinese officials have warned that they could detain U.S. citizens following the U.S. government’s prosecution of scholars affiliated with the Chinese military, though there is no indication that is connected to Friday’s arrests.

The Trump administration, which oversaw the worst dip in U.S.-China relations in a half-century, warned Americans in September to avoid travel to the country for several reasons, including its alleged detentions of citizens of other countries “to gain bargaining leverage over foreign governments.”

Although it was unclear why authorities broke up the birthday party, Shih said that people detained in drug-related cases can be held overnight. “It is the practice of Chinese law enforcement not to release detainees from a drug roundup until their tests have come back negative,” she said.

Gerry Shih and Lily Kuo contributed to this report.