Israel-Gaza updates: IDF says officer and soldier injured in attack from Lebanon

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

Reaction from Hamas and its allies was swift, with Musa Abu Marzouq, a member of the Hamas political office, saying in a statement, "The assassination of Ismail Haniyeh, the head of the Hamas Political Bureau, is a cowardly act and will certainly not go unanswered."

Islamic Jihad also issued a statement, saying the death of Haniyeh will not deter them.

Mahmoud Abbas, president of the state of Palestine, said he strongly condemned the assassination of Haniyeh, calling the attack "a cowardly act."

-ABC News' Will Gretsky

Ismail Haniyeh, the political leader of Hamas, has been killed in Tehran along with his bodyguard, Iran’s Islamic Revolutionary Guard Corps has said in a statement.

There has been no claim of responsibility for the attack at this stage.

Haniyeh was killed in his home in Tehran after participating in the inauguration of the new Iranian president, according to Hamas.