Fears of a full-scale war in the Middle East were further stoked as Iran warned it would defend itself after Israeli airstrikes killed at least four Iranian soldiers.

The International Atomic Energy Agency confirmed that no nuclear sites in Iran were hit. Israel warned that Iran would "pay a heavy price" if it responded to the strikes, while the United States, Germany and Britain demanded that Tehran not escalate the conflict further.

U.S. President Joe Biden expressed hope that "this is the end" after the pre-dawn Israeli strikes, noting that "it looks like they didn't hit anything other than military targets."

The European Union called for all parties to exercise utmost restraint to avoid an "uncontrollable escalation." Other countries, including many of Iran's neighbors, condemned Israel's strikes and urged both sides to show restraint.

Iran insisted it had the "right and the duty" to defend itself.

"While reserving its legal and legitimate right to respond at the appropriate moment, Iran is prioritizing the establishment of a lasting ceasefire in Gaza and Lebanon," the Iranian Armed Forces General Staff said.

Israel is already engaged in combat on two fronts. Since last month, it has been fighting a war against Hezbollah in Lebanon, including strikes that have killed the group's senior leadership and ground incursions aimed at destroying missile sites.

For more than a year, following Hamas's October 7, 2023, attack, Israel has also been waging a war in Gaza, resulting in mass civilian casualties in the densely populated Palestinian territory.

The United Nations has warned that the "darkest moment" of that conflict is unfolding, with Palestinians facing a dire humanitarian crisis amid daily Israeli bombings.

Stephanie Eller, deputy head of the International Committee of the Red Cross in Gaza, described the situation in northern Gaza as "horrific" during a press briefing on Saturday.

"Ongoing evacuation orders and continued restrictions on essential supplies leave the remaining civilian population in north Gaza in horrific circumstances," Eller said. "Hospitals have been ordered to evacuate, which could result in the potential loss of medical services for many civilians who remain there, while those hospitals are already struggling with severe resource shortages as more wounded and sick people continue to arrive," she added.

Eller called for further efforts to ensure safe access for humanitarian and medical personnel to reach those in need in Gaza City and northern Gaza.

The Israeli military's ground operations in Jabalia Camp, one of the largest Palestinian refugee camps, have continued for 22 days, with the stated aim of preventing Hamas from regrouping for further attacks.

(With input from agencies)