The United States said it was working "around the clock" to avert an all-out war in the Middle East, as Israel remained on high alert Tuesday for potential Iranian retaliation for two high-profile killings. US President Joe Biden, whose country has sent extra warships and fighter jets to the region in support of Israel, held crisis talks on Monday with his national security team. Biden and his top diplomat Antony Blinken sought to calm tensions that have soared since a suspected Israeli attack in Tehran last Wednesday killed Ismail Haniyeh, the political leader of Palestinian militant group Hamas.

Biden called King Abdullah II of Jordan, which helped down Iranian drones and missiles in an attack on Israel in April, while Blinken called top officials in Qatar and Egypt, the key intermediaries seeking a ceasefire in the 10-month Israel-Hamas war in Gaza. "We are engaged in intense diplomacy, pretty much around the clock, with a very simple message -- all parties must refrain from escalation," Blinken said after joining other top officials in a White House meeting. Iranian President Masoud Pezeshkian hit out on Monday at what he called the "criminal acts" of Israel "against the oppressed and defenceless people of Gaza" as well as Haniyeh's killing.

"The Islamic Republic of Iran is in no way seeking to expand the scope of war and crisis in the region, but this regime will definitely receive the response for its crimes and arrogance," Pezeshkian said during talks with a senior vis.