Israel's shelling of an Egyptian border position is stoking already existing tension between the two former enemies, who are now at sharp odds over the Israel-Gaza war, Egyptian security officials said.
The shelling which happened shortly after 5pm on Sunday injured nine soldiers, including three officers. Two of the injured are in a serious condition, the officials added, and one of the three officers is a colonel. Israel described the incident as "accidental".
Egypt and Israel are bound by a historic peace treaty signed in 1979, ending 25 years of enmity that saw them fight four full-fledged wars between 1948 and 1973. Relations were dubbed a “cold peace” for three decades before the two began to forge close energy and security ties in recent years.
The Israeli military said that one of its tanks had “accidentally fired and hit an Egyptian post” near the border with Gaza, which is the target of a devastating air campaign by Israel in response to a deadly rampage by Hamas militants on October 7 that killed 1,400 people, including women and children.
The Israeli bombardment of Gaza has killed more than 5,000 Palestinians, displaced more than a million of Gaza's 2.3 million residents and demolished entire neighbourhoods in the tiny Mediterranean enclave.
“The [Israeli military] expresses sorrow regarding the incident,” an army statement said. “The incident is being investigated and the details are under review,” it added.
The Egyptian army said Israel had “immediately expressed its regret over the unintentional incident and an investigation is under way”.
The Egyptian officials said troops deployed on the border with Israel have been instructed after Sunday's incident to “exercise maximum restraint.”
Egyptian security forces in Sinai have been put on high alert since the Israel-Gaza war began.
Sunday's accidental shelling follows what Egypt says are four incidents since the war began where Israel bombarded the Gaza side of the Rafah border crossing in the northern part of the Sinai Peninsula.
The strikes had rendered the crossing inoperable and Egyptian teams have repaired the facility at least once before the first batch of humanitarian aid was sent to Gaza on Saturday.
The Egyptian officials said Israel's air strikes appeared designed to stop the dispatch of humanitarian supplies from Egypt to Gaza without Israel's prior approval.
In one incident, Egypt said that Israel struck when several lorries laden with fuel approached the 1.5-kilometre no-man's land between Egypt and Gaza. The lorries, which were not hit, quickly retreated to the Egyptian side of the crossing.
In theory, Israel has no jurisdiction over the Rafah border crossing, which is jointly run by the Egyptian and Hamas governments. However, Israel, which ended its 38-year occupation of Gaza in 2005, wanted to have a say in what is sent to Gaza to deny Hamas of what it says is material of dual use.
Israel, in the meantime, placed Gaza under a total blockade following the October 7 attack, denying it water, electricity, fuel and food.
Humanitarian aid began entering Gaza from Egypt on Saturday following what Egyptian President Abdel Fattah El Sisi said was an agreement hammered out with US President Joe Biden and Israel. So far, at least 37 lorries have been dispatched to Gaza, carrying food, medical equipment and supplies as well as medicine.
The UN said that the aid sent to Gaza so far constituted only a small fraction of what is needed to stop it from sliding into a major humanitarian disaster.
Sunday's incident and the air strikes targeting the Rafah crossing come at a time when anti-Israeli sentiments are running high in Egypt. Tens of thousands of protesters, including university students and activists, have rallied against Israel in the past week and two pro-government lawmakers publicly called for war against Israel.
“Egypt has paid very dearly for the sake of peace in this region, it initiated it when the calls for war were loudest and it maintained it alone,” President El Sisi, a former army general, told an international gathering in Egypt on Saturday.
“Egypt held its head high as it lead the region towards peaceful coexistence based on justice,” he added.