At Columbia University on Thursday, two groups of hundreds of students tensely faced each other in dueling pro-Israel and pro-Palestinian demonstrations, while university officials blocked public access to the New York City campus as a safety measure.

Supporters of Palestinians, many of whom wore face masks to hide their identities, held signs in a grassy area near a library that read "Free Palestine" and "To Exist is to Resist." About 100 feet (30 meters) away, students backing Israel silently held up posters with the faces of Israeli hostages taken by Hamas.

After the Palestinian militant group Hamas' weekend attack on Israel, Israel has bombarded and laid siege to the Gaza Strip, controlled by Hamas, and plans a ground invasion. The Israeli death toll had risen to more than 1,300, according to public broadcaster Kan. Gaza authorities said more than 1,500 Palestinians had been killed.

Amid the growing conflict, tensions between students on opposite sides of the issue have boiled over on some U.S. college campuses.

Statements by student groups supporting Palestinians have prompted outrage and fear among Jews and, in some cases, wider rebuke from public officials and corporations. There have been reports of harassment and assaults of both pro-Israel and pro-Palestinian students, deepening grief and putting students of all political stripes on high alert.

"Jewish students are afraid," said David Hidary, a 20-year-old physics major, who attended the Columbia protest with an Israeli flag draped over his shoulders.

In a sign of the tensions, some counter-protesters at Columbia shouted angrily at the pro-Palestinian group. During a moment of silence for Palestinian victims, an opposing protester yelled out that they should be honoring children murdered by Hamas.

Several masked speakers at the pro-Palestine rally declined to reveal their full names, with one saying they did not feel safe enough on campus to disclose their identity. Many faulted the university for not expressing more support for Palestinian students and the people of Gaza.

The campus climate may only become more tense in coming days. Israel has vowed to annihilate Hamas in retribution for the deadliest attack by Palestinian militants in Israeli history.

Meanwhile, college administrators are grappling with how to keep campuses secure and denounce the violence in the Middle East without wading too deeply into a supercharged political and historical dispute that affects Jewish and Palestinian students personally.

'Day of resistance' called

A controversy at Harvard University on Monday was one of the first to make headlines. Prominent alumni lambasted a joint student group statement calling Israel "entirely responsible" for the war. The university president later clarified that the groups did not represent the school's position.

On Tuesday, the names and personal information of students allegedly involved were posted online and on Wednesday a billboard truck displaying that information was driven around campus, the Harvard Crimson newspaper reported. Some critics of the pro-Palestinian letter responded by denouncing the intimidation of students, the newspaper said.

Tensions sparked anew at campuses on Thursday as the national group Students for Justice in Palestine (SJP) declared a "day of resistance," with demonstrations by its 200 chapters at colleges across North America.

The national group, which advocates for an independent Palestine and says on its website that it promotes "an agenda grounded in freedom, solidarity, equality, safety and historical justice," called the October 7 attack by Hamas "a historic win for the Palestinian resistance."

The Anti-Defamation League, a nonprofit organization fighting antisemitism, wrote a letter to college presidents warning that Students for Justice in Palestine was "condoning terrorism by Hamas by repackaging it as justified acts of 'resistance'" with its planned day of action.

The University of Arizona, Tucson chapter of SJP canceled a protest on Thursday, citing safety concerns after the school's president called the gathering "antithetical to our university's values."

Dozens of students from the University of California Los Angeles chapter of SJP held a march for Palestine on Thursday, despite the group's report that its student members had been harassed and assaulted over the last several days, including while counter-protesting a pro-Israel rally.

At Georgetown University in Washington, DC, the SJP chapter chose to host a vigil on Thursday night but declined to allow media access "due to increased harassment and threats of violence against Palestinian, Arab, Muslim and anti-Zionist students across the country."