US President Joe Biden has said that the assassination of Hamas leader Ismail Haniyeh “doesn’t help” talks over a potential ceasefire in Gaza.
Haniyeh was killed during a visit to Iran’s capital, Tehran, on Wednesday. Iran and its allies have blamed Israel, although Israel is yet to comment on his death.
Haniyeh was Hamas’s most senior official and was highly involved in ceasefire and hostage release talks from his base in Qatar.
Mr Biden said he was “very concerned” about rising tensions in the Middle East. "We have the basis for a ceasefire. He [Israeli Prime Minister Benjamin Netanyahu] should move on it and they [Hamas] should move on it now."
Israel and Hamas recently resumed tentative, indirect talks to try to reach a ceasefire in the war in Gaza, though there have been conflicting accounts of progress.
At the end of May, Mr Biden outlined what he said were the terms of an Israeli ceasefire proposal. This has become the basis for on-off indirect negotiations between Hamas and Israel since then, with Qatar, Egypt and the US acting as mediators.
Earlier this week, Israel and Hamas accused each other of obstructing progress. Hamas said Israel had introduced new conditions, while Mr Netanyahu's office said Hamas had demanded 29 changes to the proposal.
The war began in October when Hamas carried out an unprecedented attack on Israel, killing about 1,200 people and taking 251 others back to Gaza as hostages. The attack triggered a massive Israeli military response, which has killed at least 39,480 Palestinians in Gaza, according to the territory's Hamas-run health ministry.
Mr Biden's comments were his first on Haniyeh's assassination since the Hamas chief was killed.
The US president spoke to journalists at Andrews Air Force Base in Maryland, ahead of welcoming home American citizens as part of a prisoner exchange with Russia.
He said he had spoken to Mr Netanyahu earlier on Thursday and had promised to protect Israel "against all threats from Iran", which has vowed to retaliate. Iran is Hamas's most important backer and is an arch-foe of Israel.
Israel has not claimed responsibility for the assassination, but Mr Netanyahu said after the killing that Israel had delivered “crushing blows” to Iran’s proxy groups in recent days.
Haniyeh’s assassination came at a time of soaring tensions in the Middle East.
On Saturday, 12 children and young people were killed after a strike on a football field in the Israeli-occupied Golan Heights. Israel blamed Lebanon's Iranian-backed Hezbollah movement and vowed "severe" retaliation, though Hezbollah has denied involvement.
On Tuesday, hours before the killing of Haniyeh, Israel killed senior Hezbollah commander Fuad Shukr, who it said was behind the attack on the Golan Heights, in a targeted air strike in Beirut.