The strike that killed Ismail Haniyeh came just hours after Israel said it had assassinated a top Hezbollah commander in a strike on the Lebanese capital Beirut.

The killings took place as regional tensions were already inflamed by the war in Gaza, a conflict that has drawn groups in Syria, Lebanon, Iraq and Yemen.

Israel has declined to comment on the Tehran strike.

Speaking in the Mongolian capital, top US diplomat Blinken warned the Middle East was on a path "toward more conflict, more violence, more suffering, more insecurity, and it is crucial that we break this cycle".

"That starts with a ceasefire that we've been working on," Blinken told reporters alongside his local counterpart.

"And to get there, it also first requires all parties to talk, to stop taking any escalatory actions, it requires them to find reasons to come to an agreement," he said.

As he did on Wednesday in Singapore, Blinken did not comment directly on the assassination of Haniyeh.

He also declined to speculate on the impact that Haniyeh's killing could have on a potential ceasefire in Gaza, which the United States has been spearheading along with Egypt and Qatar.