Israel's relentless war against Hamas, the Palestinian militant group that rules the Gaza Strip, is leading to increasingly strained ties with Egypt.

Relations between the two states have taken a turn for the worse since Israeli troops seized control of the Hamas-controlled side of the Rafah border crossing between Gaza and Egypt on May 6. 

In photos that have since gone viral, Israeli soldiers can be seen raising the Israeli flag near the border crossing.

Since then, Egypt has kept its side of the border shut and has said it will remain closed as long as Israeli troops are on the Gaza side. It has also said it will no longer cooperate with Israel to transfer humanitarian aid and will only reopen the crossing if the Rafah side comes under Palestinian control again.

On Thursday, Israel said it would be sending more troops into Rafah, and Israeli Prime Minister Benjamin Netanyahu argued that the capture of the crossing was "an important step toward dismantling Hamas' military and governing capabilities."

Egypt 'driven by anger and frustration'

"Egypt strongly condemns the occupation of the border crossing," Simon Wolfgang Fuchs, an associate professor at the Hebrew University of Jerusalem, told DW. "Egypt's current reactions are driven by anger and frustration."

He explained that since Israel's military campaign in Gaza in response to the unprecedented attack launched by Hamas on October 7, Egypt had been very cooperative and had meticulously adhered to all of Israel's conditions regarding the inspection of humanitarian aid deliveries via the Rafah border crossing into Gaza. Therefore, he pointed out, "Cairo expected to be treated with respect."

However, according to Egyptian intelligence officials, Israel only informed Cairo hours before it took control of the border crossing, with a brief message.

The officials said Israel had failed to keep previous promises that the joint border crossing would not be affected by Israel's ongoing operation in Gaza.

Mohamed Anwar Sadat, the nephew of the Egyptian president of the same name who negotiated the Camp David Accords that led to the Egypt-Israel peace treaty of 1979, told The Wall Street Journal this week that the current dispute was the worst bilateral crisis the two states had seen.

He said that there was "now a lack of trust," and suspicion on both sides.

"Egypt definitely considers the Israeli concentration of troops on the border as a potential long-term security concern," said Nathan Brown, a professor of political science and international affairs at George Washington University in Washington.

He told DW that for almost half a century "the Camp David Accords between Egypt and Israel and the subsequent peace treaty" had limited Egyptian military deployment in Sinai, in Egypt's north, close to the border with Gaza and Israel.

Now, for the first time since 1979, this could be changing as unconfirmed sources have said Egypt recently started to deploy troops and equipment to Sinai.

Cairo fears Palestinian exodus into Egypt

Other observers have pointed out that ties had been strained even before Israel seized the Rafah border crossing, over fears Israel's offensive in Gaza could cause a Palestinian exodus into Egypt.

Egyptian President Abdel Fattah el-Sissi has repeatedly warned that this would be a "red line" and that his country — whose population largely supports the Palestinians and the two-state-solution — will not take in Palestinians fleeing Gaza.

So far, the conflict in Gaza has killed more than 35,000 people, according to the Hamas-run Health Ministry. 

In April, around 1.6 million internally displaced people — of Gaza's population of 2.3 million — sought refuge in Rafah after Israel's military advised civilians to flee from other parts of the enclave.

But this month, in anticipation of its announced invasion of Rafah, the military ordered hundreds of thousands of people in the city to leave.

Some 600,000 people fled toward the city of Khan Younis and further north along the beach where tent camps have been set up, according to the United Nations. 

Netanyahu has said the operation is necessary to destroy the remaining Hamas battalions in Rafah. Hamas is classified as a terrorist group by Israel, the US, Germany and other governments.

"The Israeli-ordered evacuations of people to new so-called 'humanitarian zones' have swept aside Egypt's concerns of an exodus for the time being," said Simon Wolfgang Fuchs.

"But of course, Egypt knows that this does not mean that the danger has been averted, and if the humanitarian situation continues to be as dramatic and difficult as it is now, a storming of the border could still be in the offing."

Egypt taking symbolic steps to show its 'displeasure'

"Egypt wants to communicate to Israel very, very clearly that it does not want to be taken for granted," said Brown, adding that over the past weeks, it had become clearer that Egypt was prioritizing its own interests.

"Cairo's concern is that the war between Israel and Hamas will create problems for Egypt," he added. The government, which maintains relations with Hamas and Israel, has now said it will reconsider its mediating role over the release of the Israeli hostages held by Hamas and a cease-fire in Gaza.

The Egyptian government is also contemplating recalling Khaled Azmi, Egypt's ambassador in Tel Aviv, according to a report in The Wall Street Journal.

On Sunday, Egypt said it would join South Africa's genocide case against Israel at the International Court of Justice in The Hague.

"The joining of the ICJ case communicates displeasure in a very direct and even visceral way to the Israeli leadership," said Brown said.

Timothy E. Kaldas, deputy director of the Washington-based Tahrir Institute for Middle East Policy, said he did not think Egypt would cut ties with Israel altogether. 

"Egypt has plenty of other ways to communicate displeasure without escalating to the point of abrogating the peace treaty with Israel," he said.

Observers have pointed out that it's important for Egypt to maintain the peace deal with Israel, as this will allow bilateral trade between the two states to continue to flourish. In particular, Egypt depends on gas imports from Israel, and is also does not want to risk much-needed military support from the US.

DW's Emad Hassan contributed to this article.