Blinken says US 'not aware of or involved in' Hamas chief Ismail Haniyeh's assassination by Israel

US Secretary of State Antony Blinken said Wednesday that the United States was "not aware of or involved in" the killing of Hamas's political leader Ismail Haniyeh in Iran.

"I can't tell you what this means. I can tell you that the imperative of getting a ceasefire, the importance that that has for everyone, remains," Blinken said in an interview with Channel NewsAsia in Singapore.

"This is something we were not aware of or involved in," he said of the killing.

Haniyeh was in Iran to attend the inauguration of Iran's new president when he was killed by an Israeli air strike, Hamas said Wednesday.

Washington is Israel's key military backer and has been pushing for a Gaza ceasefire, which Blinken said remains "manifestly in the interests" of the Israeli hostages and Gazans who have been "caught in this crossfire of Hamas's making". Critics say the US has not done enough to pressure Israel into accepting the ceasefire, while Hamas has accepted it on numerous occasions. 

As the political chief of the Palestinian movement Hamas, Haniyeh was overseeing the negotiations for a deal to end the war in Gaza and release hostages held in the territory in exchange for Palestinian prisoners detained by Israel.

Blinken, who is visiting Singapore, said a Gaza ceasefire was also essential to prevent the conflict from spreading to the rest of the region.

"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 told a forum in the city-state.

"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 ceasefire."

Qatar -- a vital mediator in truce talks which also hosts Hamas's political leadership that included Haniyeh -- has questioned the future of negotiations in the wake of the assassination.

Blinken spoke with Qatar's Prime Minister Sheikh Mohammed bin Abdulrahman Al-Thani on Wednesday and emphasised "the importance of continuing to work to reach a ceasefire", State Department spokesman Matthew Miller said.

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