The United States was "not aware of or involved in" the assassination of Hamas' political leader Ismail Haniyeh in Iran, Secretary of State Antony Blinken said Wednesday.

"This is something we were not aware of or involved in," Blinken said, according to a transcript shared by his staff from an interview with Channel News Asia in Singapore.

He added, however, that killing made a cease-fire in Gaza all the more "imperative."

Speaking at a forum in Singapore he said that reaching a ceasefire in Gaza "is the enduring imperative".

"We've been working from day one not only to try to get to a better place in Gaza but also to prevent the conflict from spreading, whether it's the north with Lebanon and Hezbollah, whether it's the Red Sea with the Houthis, whether it's Iran, Syria, Iraq, you name it," Blinken said.

"A big key to trying to make sure that that doesn't happen and that we can move to a better place, is getting the cease-fire."

Haniyeh was attending the inauguration of Iran's new president when he was killed by an Israeli airstrike, Hamas said Wednesday.

Hamas blamed Israel and vowed the "cowardly" killing of their veteran leader "will not go unanswered."

Israeli Prime Minister Benyamin Netanyahu has vowed to destroy Hamas in retaliation for its Oct. 7 incursion of Israel, which sparked Tel Aviv's genocidal war on Gaza.

The Oct. 7 incursion resulted in the deaths of 1,197 people, mostly civilians, according to an AFP tally based on official Israeli figures.

Palestinian resistance groups also seized 251 hostages, 111 of whom are still held captive in Gaza, including 39 the military says are dead.

Israel's brutal military campaign has killed nearly 40,000 people in Gaza, according to the Health Ministry.

Blinken said achieving a cease-fire was "manifestly in the interests of the hostages and bringing them home, it's manifestly in the interests of Palestinians who are suffering terribly every single day, children, women, men in Gaza."

"... it's profoundly in the interest of trying to put things on a better path not only in Gaza, but actually throughout the region, because so much is tied to what's happening in Gaza right now," he said.