The blast which killed Hamas' political leader Ismail Haniyeh in Tehran was met with vows of revenge from Iranian leaders, including Ayatollah Ali Khamenei, who blamed Israel's "criminal, terrorist Zionist regime" for the "bitter, tragic event."

By killing Haniyeh, Israel has "prepared the ground for a severe punishment," Khamenei said on his website, adding that "we believe it is our duty to take revenge."

Israel has not taken responsibility for the strike.

Haniyeh had been on a high-profile visit to Iran when he was killed. He was hoping to reaffirm Tehran's support to Hamas in the war against Israel.

On Tuesday, he met with Khamenei and attended the inauguration of Iran's new president, Masoud Pezeshkian, and even posed for defiant photos in the parliament.

Then, he was taken to a special residence in north Tehran under high security, only to be assassinated in an apparent surgical strike overnight. One other person — his Palestinian bodyguard — is believed to have been killed.

Iranian secret services ridiculed

On Iranian social media, the reaction seemed to be leaning less toward anger and more toward mockery of the country's vast security apparatus for failing to prevent the strike. 

"In the middle of Tehran, under the nose of dozens of institutions and thousands of security agents, on the most important day of the government, the most important guest of this government has been assassinated and killed," human rights defender and political journalist Mehdi Mahmoudian wrote in an online post.

He, like many others, mocked the security services for being vigilant on other issues — such as hijab violations — while allowing high-profile hits such as the one in Tehran, which came just hours after Israel targeted top Hezbollah commander Fouad Shukur in Beirut.

Both Hamas and Hezbollah are considered terror groups by the US, Germany and many other countries. Both are backed by Iran, although Hezbollah, which is a Shiite group and particularly loyal to Ayatollah Khamenei, is considered a more valuable partner than Hamas.

Middle East on edge

The two killings have put Iran under enormous pressure to strike back at Israel, whom the regime blames for the attacks on its allies.

The regime supporters want Tehran to retaliate: "If Tehran doesn't respond now, it will be mocked by domestic audiences, while no other guests from the Axis of Resistance — especially (top Hezbollah leader Hassan) Nasrallah or other Palestinian officials — would come to Tehran anymore," regime-friendly journalist Fereshteh SadeghI wrote online.

Daniela Sepehri, an Iranian human rights activist based in Berlin, counters this pro-regime sentiment by saying that "the fact that the Hamas terrorist Haniyeh was eliminated in Tehran is extremely embarrassing for the regime."

"They (the Iranian regime) were not even able to protect their closest ally in their own country. The first day of work for the new president Masoud Pezeshkian starts with an embarrassment for terrorists and a partial victory for the freedom movement," Sepehri told DW.

"Hamas is a terrorist organization that is ideologically, financially and militarily supported by the Islamic Republic of Iran and is responsible for terror against Israel and Palestine," she added.

Iran's next step remains unclear beyond general calls for retaliation.

While deciding on a response, Iranian leaders will need to take into account all possible reactions from Israel. The region is already on the brink over the Israel-Hamas war in Gaza, and while Iran is willing to provide support to Hamas, Hezbollah and Houthi rebels for limited moves against Israel and the West, it has so far attempted to avoid a full-scale war. A direct attack on Israel could see the US step in to protect its closest ally and in turn threaten the survival of the Islamic regime.

Instead, Iran could attempt to launch a tit-for-tat attack on Israeli officials, or use its regional proxies to hit targets in Israel.

No safety in Iran

Strategic analyst Damon Golriz told DW that the only way to avoid a regional war would be for Washington to reaffirm "its ironclad commitment to Israel's security by signifying its military muscle in the region" and "creating real deterrence to Iran."

Even without the US and Iran coming to blows, the Iranian regime would face renewed displeasure from its own population if its military adventures escalated.

British-Iranian journalist Shahran Tabari said that ordinary Iranians "have no animosity with the people of Israel or Palestine" and are unwilling to support the likes of Hamas and Hezbollah.

She predicted that the regime would "try to back off but (it is) not obvious it will succeed."

Finally, the latest bombing in Tehran puts Iranian leaders in a particularly risky double-bind. If their claim about Israel being behind the attack turns out to be correct, the Tehran strike also sends a message that Israel is capable of targeting any Iranian leader, wherever they are. This may give them pause in planning a large-scale attack — but Iranian officials could just as likely decide that a severe response will serve as a deterrence and protect them from similar attacks in the future.

DW's Farsi department contributed to this report.

Edited by: Shamil Shams

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This article has been updated to reflect the state of Israel-Hamas war in Gaza and its impact on the Middle East, and to specify Fereshteh SadeghI is a source considered close to the Iranian regime as well as to add rights activist Daniela Sepehri's statement.