Outcry has steadily risen in Türkiye since Hamas leader Ismail Haniyeh was assassinated in the Iranian capital Tehran early Wednesday, with officials and citizens alike denouncing it as a "heinous" act and calling for action to stop Israel, which is widely blamed for the attack.

Hamas said Haniyeh was killed in an Israeli strike in Tehran while visiting for the inauguration of Iranian President Masoud Pezeshkian, in an act that has stunned the international community. Israel has not commented on the death, but Prime Minister Benjamin Netanyahu has hinted at Israel’s involvement.

Haniyeh, normally based in Qatar, had been the face of Hamas' international diplomacy as Israel has waged war on Gaza. He had been taking part in internationally brokered indirect talks on reaching a cease-fire in the Palestinian enclave.

"It seems impossible for Israel to take any steps on especially a cease-fire without any cost," Foreign Minister Hakan Fidan warned late Wednesday on his way to Türkiye from Tehran.

"It’s the United States and the West that will make Israel pay that price," Fidan told Turkish newspaper Sabah’s Okan Müderrisoğlu. "There has to be a restriction, an accusation. When powers that rein the global system are passive, Israel goes as far as it can."

The international community has since called for de-escalation and a focus on securing a cease-fire in Gaza – which Haniyeh had, according to a Hamas official previously, accused Israel of obstructing.

Ankara has condemned the assassination and accused Israel of wanting to expand the war in Gaza to the entire region with Haniyeh’s killing.

President Recep Tayyip Erdoğan, who often referred to Haniyeh as a "brother," met the Hamas chief in Istanbul as recently as April. "His assassination will not break the Palestinians’ will," he said after the news.

Separately on Thursday, he vowed Türkiye would "not give the opportunity to those who want to turn our region into a bloodbath, and we will continue to be a source of trust for our own citizens and our friends."

Cease-fire odds dim

Haniyeh’s killing came hours after Israel killed a top Hezbollah commander in Lebanon and retaliated against Yemen’s Houthi rebels, enflaming fears of a wider regional war and decimating any chance of peace.

"In order to prevent incidents like this, there needs to be a two-state solution," Fidan argued, echoing Ankara’s commitment to a sovereign Palestinian state with 1967 borders and East Jerusalem as its capital.

Pointing out that Arab states are usually the addressee when it comes to Palestine, Fidan said Türkiye has "striven to make an individual effort" in recent years, approaching the issue with a "solution-oriented, inclusive outlook."

"If there will be any impact, this is how it happens," Fidan said.

Türkiye is a staunch supporter of Hamas, which it describes as a resistance movement, unlike the Western countries which mostly define it as a terrorist group.

The country has denounced Israel's attacks on Gaza after last year's offensive by Hamas. It has called for an immediate cease-fire and regularly criticizes what it calls unconditional support for Israel by the West.

Ankara also has halted all trade with Israel and said it had decided to join South Africa's initiative to have Israel tried for genocide at the International Court of Justice (ICJ).

According to security sources on Thursday, the National Intelligence Organization (MIT) too has played a key role in resolving the deadlocks in Gaza cease-fire negotiations and bringing Israel, Hamas and key brokers Qatar, Egypt and the U.S., closer to a common point.

"However, Haniyeh’s death in a planned Israel attack has disrupted the peace expected to reach Gaza right when negotiations to end the war were nearing a conclusion," Turkish security sources said.

"The assassination proves Netanyahu has no desire for a cease-fire or intention to end the clashes," they added.

U.S. Secretary of State Antony Blinken on Thursday reiterated appeals for an end to fighting. He said achieving peace "starts with a cease-fire" and called on "all parties" to "stop escalatory actions."

But the prime minister of Qatar said Haniyeh's killing had thrown the whole Gaza war mediation process into doubt.

Fidan similarly said the world has become used to Israel’s everyday massacres in Gaza, which he warned was a "dangerous" thing.

"We are no longer close to a cease-fire," he lamented. "There is nothing to push Israel to a cease-fire."

Public rallies

Fidan also touted pro-Palestinian demonstrations from the Turkish public and argued that Turkish nongovernmental organizations must contact their counterparts to "send a message to the world."

Rallies have been widespread across Türkiye since Oct. 7, with hundreds of thousands of citizens protesting Israel and its military backer the U.S. for months on end.

Thousands of protestors took to the streets of Istanbul late on Wednesday to condemn the killing of Haniyeh. The demonstrators held posters with Haniyeh's photos and banners reading, "Martyr Haniyeh, Jerusalem is our cause and your path is our path."

Protesters were chanting "murderer Israel, get out of Palestine," "thousands of greetings from Istanbul to the resistance in Gaza" and waving Turkish and Palestinian flags during the march in the Fatih district of Istanbul.

Trying Israel

As for the genocide case at the ICJ, Fidan assured Türkiye would submit its application to the world court in a week, which would be a first for the country.

"The document’s approximately 40 pages long," he said. "Pressuring the ICJ and sharing these steps with others is important. The more qualified and legally binding this document is the fewer places (Israel) can escape to."

Ankara has employed a crew of local and international jurists specifically for the case and sent a file of evidence to The Hague earlier this year listing Israel’s war crimes, obtained on-site from Gaza.