For weeks, talk show hosts and newspaper columnists across Egypt’s government-managed media spoke with one voice: Any Israeli “occupation” of a buffer zone on the Egypt-Gaza border could violate Egypt’s sovereignty and national security. That would deal a further blow to a relationship that Israel’s offensive had already pushed to its lowest point in decades.

But when Israel’s military said last week that it had taken “tactical control” of the zone, known as the Philadelphi Corridor, the same government mouthpieces were quick to say that the area had nothing to do with Egypt. Sovereignty went unmentioned.

It was the latest indication that for all the hard feelings and security fears provoked by Israel’s devastating campaign in the Gaza Strip, Cairo sees little choice but to protect its 1979 peace treaty with Israel. The accord has generated valuable military and intelligence cooperation against Egyptian insurgents and natural gas imports from Israel, as well as a close relationship with the United States and billions of dollars in American aid.

For Israel, too, the “cold peace” with Egypt has been an essential pillar of national security for 45 years. It has given Israel a path to better relations with Arab countries, some of which have normalized their ties, making Israel an increasingly integral part of a regional, anti-Iranian axis. For the same reasons, the United States also considers the treaty, which grew out of the Camp David Accords, crucial to regional stability.

Still, Israel took the risk of upsetting that delicate balance, saying that it must control the narrow buffer zone between Gaza and Egypt for its own security. Israel says it needs to destroy dozens of tunnels under the border that have enabled Hamas to smuggle in arms — despite Egypt’s avowals that had stopped the smuggling years ago.

The Israeli military’s push into southern Gaza and the city of Rafah in recent weeks has seriously strained ties with Egypt, raising questions about how far Israel will go in insisting on control over the Philadelphi Corridor, and how much of a continued Israeli presence there Egypt will tolerate.

Hussein Haridy, the former head of Israeli affairs at Egypt’s foreign ministry, said Israel’s occupation of the area, with troops “only meters” from the border, amounted to “a direct threat to Egyptian national security.”

Egypt, he added, is deeply suspicious that Israel plans to maintain some degree of control over the border permanently.

“It becomes even more threatening since there’s no withdrawal timetable or commitment to withdraw,” he said.

Israel, with the United States’ backing, has pressed Egypt to heighten security at its border with Gaza by building a high wall extending below ground, with sensor systems that would alert both the Israeli and Egyptian militaries to tunneling and smuggling, according to Mohammed al-Zayat, an analyst at the state-linked Egyptian Center for Strategic Studies, as well as Israeli security experts.

But Egypt fears that such alarms could draw Israeli military action along the border. The presence of Israeli troops there risks further angering the many Egyptians who are already upset about what they perceive as their country’s weakness in the face of the Israeli takeover, and who still regard Israel as an enemy.

With Israel troops on the border, Egypt sees a growing prospect of Israel pushing Gazans to flee, creating a refugee crisis within Egypt, giving Hamas a foothold there and potentially endangering hopes for a future Palestinian state. And Egypt wants to show both its own people and its foreign partners that its military-dominated regime, which took power promising security and stability, is competent enough to manage the border by itself.

The 1979 peace treaty is “the cornerstone of Egyptian foreign policy, it’s the whole justification of the $1.3 billion that the Americans give the Egyptians every year,” said Riccardo Fabiani, an Egypt analyst at the International Crisis Group. “So if somebody says the Egyptians aren’t reliable, you can’t trust the Egyptians when it comes to this very delicate border, this whole thing comes apart.”

Israel’s takeover of the Philadelphi Corridor leaves Egypt feeling threatened, with few cards to play.

To convey its displeasure, Cairo has registered to speak in support of South Africa’s case at the International Court of Justice accusing Israel of committing genocide in Gaza. It has also warned that Israel is jeopardizing the treaty.

Though it has denounced Israel for cutting off humanitarian aid to Gaza, Egypt itself took the extreme step last month of temporarily suspending the flow of supplies from its own territory in an attempt to force the United States to pressure Israel into withdrawing from the Rafah border crossing with Egypt. The sight of the Israeli flag flying over that border point, the main conduit for aid and other goods during the war, had drawn public outrage in Egypt.

But Egypt has refrained from taking more serious steps against Israel. Unlike Jordan, it has not withdrawn its ambassador from Tel Aviv.

“No one is interested in any kind of escalation, so I believe they will find a solution to satisfy the Israeli side,” said Mohamed Anwar el-Sadat, an independent Egyptian politician and the namesake nephew of the president who signed the 1979 treaty. “It’s in both our interests to reach an understanding or agreement to avoid any kind of confrontation.”

The government-managed news media appears to have been helping with efforts to limit public outrage.

Before Israel said that it had established control of the Philadelphi Corridor, the rhetoric from news outlets verged on bellicose. Egypt is “ready for all scenarios, and will never allow any encroachment on its sovereignty and its national security, either directly or indirectly,” Ahmed Moussa, a prominent talk show host, wrote in a column for Al-Ahram, Egypt’s flagship daily newspaper, on May 17.

Yet after Israel took the corridor, Mr. Moussa was on the air, fulminating against social media users who said it made Egypt look weak. He linked such “allegations” to the Muslim Brotherhood, the political Islamist group — of which Hamas is an offshoot — that Egypt’s government has long demonized as a terrorist organization.

“The Philadelphi Corridor is not Egyptian territory,” Mr. Moussa said in a nine-minute segment devoted to the issue, displaying a giant map. “It’s Palestinian territory. It doesn’t belong to us.”

The Israeli-Egyptian relationship has weathered wars and Palestinian uprisings, the 2011 Egyptian revolution that overthrew President Hosni Mubarak, and the brief presidency of Mohamed Morsi, the senior Muslim Brotherhood leader who won Egypt’s first free elections a year later.

Rafah and the eight-mile-long Philadelphi Corridor have often served as points of connection and friction between Egypt and Israel. The two countries jointly enforced a blockade on Gaza after Hamas seized control of the coastal enclave in 2007, soon after Egypt and Israel had agreed on the number of troops that could be stationed around the buffer zone.

But the question of smuggling remained contentious. In 2005, when Israel unilaterally withdrew its forces and Jewish settlers from Gaza, many Israeli strategists said it was a mistake to abandon the corridor to the smugglers. Current and former Israeli officials say that once Hamas came to power, the Rafah crossing became a main channel for weapons smuggling, which peaked as Egyptian security broke down during Mr. Morsi’s tumultuous presidency.

But Abdel Fattah el-Sisi led a military coup that overthrew Mr. Morsi in 2013, and became president a year later. He has since forged a close security partnership with Israel over their shared interest in stamping out an insurgency in northern Sinai, the Egyptian region bordering Gaza and Israel.

Seeing Hamas as a security threat, Egypt spent years cracking down on smuggling into Gaza, destroying and flooding tunnels, and constructing walls. The Egyptian and Israeli militaries also developed strong links, including a regular communication channel to discuss smuggling, counterterrorism and intelligence sharing. Israel even agreed to allow Egypt to station more troops along the border than they had previously agreed to.

Given the Egyptian public’s deep antipathy toward Israel, neither side trumpeted their cooperation. But Mr. el-Sisi acknowledged in a 2019 interview that Egypt had “a wide range of coordination” with Israel.

That may have been the high point. When news reports surface about Egyptian-Israeli talks about the border these days, Egyptian officials are quick to deny any coordination.

Israel, however, still sees the advantages of the relationship, especially since it may need Egyptian help in managing Gaza after the war.

“There was a close strategic dialogue with the Egyptians, and we need to preserve that,” said Efraim Inbar, an expert on Israel’s strategic doctrine and president of the Jerusalem Institute for Strategy and Security.