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.