Tens of thousands of people protested across the Middle East in support of the Palestinians and in condemnation of Israel.

In Jerusalem, the Al-Aqsa Mosque was expected to be a focus of demonstrators' attention and a possible flashpoint.

From Amman, Jordan, to Yemen’s capital, Muslims poured out onto the streets after weekly Friday prayers. Tens of thousands of Iraqi protesters also gathered in Baghdad's Tahrir Square today, burning the Israeli flag, waving Palestinian flags and chanting anti-American slogans.

Authorities in the U.S., throughout Europe and elsewhere were on alert after a former leader of Hamas called for a global day of “rage” today. Such calls in the past have led to sizable demonstrations and unrest.

The Israeli Foreign Affairs Ministry said that it expressed “deep disappointment” in a call with the Chinese envoy to the Middle East over Beijing’s failure to explicitly condemn the terrorist attacks by Hamas.

“The ambassador expressed Israel’s deep disappointment with Chinese announcements and statements about the recent events in the south, where there was no clear and unequivocal condemnation of the terrible massacre committed by the terrorist organization Hamas against innocent civilians and the abduction of dozens of them to Gaza,” the statement said.

In his call Thursday with Israeli Foreign Ministry official Rafi Harpaz, China’s first public contact with Israel since the attack, Middle East envoy Zhai Jun said Beijing condemns actions that harm civilians and calls for a cease-fire and the resumption of peace talks based on a two-state solution, according to a readout published by the Chinese Foreign Ministry.

Also Thursday, Chinese Foreign Minister Wang Yi made his first public comments on the Israel-Hamas war, saying that the Palestinian issue is at the core of Middle East affairs, and that “the crux of the matter is that justice has not been done to the Palestinian people.”

TEL AVIV — For Israeli families desperate to be reunited with their loved ones who were taken hostage by Hamas, the militant group's claim today that 13 hostages died in Israeli airstrikes on the Gaza Strip comes as a new and devastating blow. NBC News has not verified Hamas' claim.

"I feel horrible," said Liel Fishbien, 25, whose younger sister, Tchelet Fishbien, 18, and her boyfriend, whom she had recently started dating, are believed to have been taken hostage by Hamas when it ambushed Be'eri on Saturday. "Horrible doesn’t even begin to describe it," he said.

He said he has not had any word about his sister since he last lost contact with her around 11:30 a.m. Saturday. He survived the incident after hiding with his grandmother at her home, but his sister and her boyfriend, who were at another residence, are believed to have been taken by Hamas.

Orly Chen, the aunt of Itay Chen, a 19-year-old believed to have taken hostage Saturday while on active duty for the Israeli military, said she hadn't heard about Hamas' claim. "I don't even know what to say. I don't know," Chen, 56, said. "It’s not easy. We’re not sleeping ... I don’t even know what’s going on. I just want my nephew."

The international charity Doctors Without Borders has accused Israel of launching “an attack on medical care and humanity” by giving residents of northern Gaza an order to leave their homes, land and hospitals.

Meinie Nicolai, director general of the charity also known as Médecins Sans Frontières, said in a statement that Israel’s evacuation order was “outrageous” and condemned it “in the strongest possible terms.”

“‘Unprecedented’ doesn’t even cover the medical humanitarian impact of this,” she said. “Gaza is being flattened, thousands of people are dying, this must stop now.”

Russian President Vladimir Putin has said a possible ground operation by Israel in the Gaza Strip would led to "absolutely unacceptable casualties."

"We hear now about preparing a ground operation. We understand how it will go. How do I put it? In a semi-professional style, use of heavy equipment in residential areas is hard to execute. This may lead to grave consequences for all the sides," Putin said.

“The most important thing is that losses among civilians will be absolutely unacceptable," he added. "There are almost 2 million people living there.”

Putin's own war in Ukraine has led to hundreds of thousands of military and civilian casualties and obliterated entire cities, to little gain for Russia's army.

President Joe Biden is expected to speak with the families of some of the Americans believed to be held hostage in Gaza today, according to a White House official.

He addressed the scheduled call with the family members in a clip released from his interview with "60 Minutes" that's airing Sunday on CBS.

"Why do you feel so strongly about speaking to these families personally?" asked "60 Minutes" correspondent Scott Pelley. Biden responded, "Because I think they have to know that the president of the United States of America cares deeply about them, deeply."

"We have to communicate to the world this is critical. This is not even human behavior. it’s pure barbarism, and we’re going to do everything in our power to get them home, if we can find them," he added.

Israel dropped leaflets over Gaza City telling residents to evacuate and move south. It came after it earlier issued the same warning to the United Nations and online.

"Gaza city has turned into a battle field," the leaflet read in Arabic, according to a translation by Reuters. "You have to leave your homes immediately and head south of Wadi Gaza. For your safety: Don’t return to your homes until further notice from the Israeli Defence Forces."

Wadi Gaza is the river that bisects the narrow strip of land.

The Israeli ambassador to the U.N., Gilad Erdan, criticized the world organization for its response to the evacuation order this morning.

"The UN’s response to Israel’s early warning to the residents of Gaza is shameful! For many years, the UN has turned a blind eye to the arming of Hamas and its use of the civilian population and civilian infrastructure in the Gaza Strip as a hiding place for its weapons and murder. Now, instead of standing by Israel, whose citizens were slaughtered by Hamas terrorists and who tries to minimize harm to those not involved, it preaches to Israel," Erda said in a statement.

"It is better for the UN to focus now on returning the hostages, condemning Hamas, and supporting Israel’s right to defend itself," he added.