Iran's Supreme Leader Ali Khamenei said his country had a "duty to take revenge" after Hamas' political leader was killed in Tehran.

"However, following this bitter, tragic event which has taken place within the borders of the Islamic Republic, we believe it is our duty to take revenge," Khamenei said Wednesday.

No country or organization has yet taken credit for the assassination, but Khamenei appeared in his statement to blame Israel, saying the "criminal, terrorist Zionist regime martyred our dear guest in our territory."

-ABC News' Morgan Winsor and Kevin Shalvey

As news of the killing of Ismail Haniyeh, the political leader of Hamas, begins to spread on Wednesday morning, global leaders have started to react, condemning his death and calling it a “heinous assassination.”

In a statement, Jordan’s Ministry of Foreign Affairs “condemned in the strongest terms Israel’s assassination of the head of the political bureau of the Islamic Resistance Movement in Palestine (Hamas), Ismail Haniyeh, may God have mercy on him, in the Iranian capital, Tehran, in violation of international law and international humanitarian law, and an escalatory crime that will push towards more tension and chaos in the region.”

Turkey’s Ministry of Foreign Affairs also condemned Haniyeh’s death, calling it a “heinous assassination” and reiterated the need to stop Israel from escalating regional tensions.

Meanwhile, Russia’s Deputy Foreign Minister Mikhail Bogdanov told state-owned RIA news agency that the killing of Haniyeh “is an absolutely unacceptable political murder, and it will lead to further escalation of tensions."

The Israeli Government Press Office posted a photo of Ismail Haniyeh with the word "eliminated" over the Hamas political leader's head. The post, which had been live for more than an hour, was then removed Wednesday morning.

"Eliminated: Ismail Haniyeh, Hamas highest- ranking leader, was killed in a precise strike in Tehran, Iran," the office said in a post on its official Facebook page.

There has been no claim of responsibility for the assassination.

-ABC News' Morgan Winsor and Helena Skinner

The death of Ismail Haniyeh, the Hamas political leader, in Iran "will strengthen the deep and unbreakable bond between the Islamic Republic of Iran and the beloved Palestine and the resistance," an Iranian state spokesperson said.

"The pure blood of Martyr Haniyeh will never be wasted," Foreign Ministry spokesperson Nasser Kanaani said, according to Iranian state media.

Iranian authorities were investigating the assassination, he said.

Kanaani praised Haniyeh for spending his life in the "honorable struggle against the usurping Zionist regime" and for seeking the "the liberation of the oppressed Palestinian nation."

-ABC News' Somayeh Malekian and Joe Simonetti