President Joe Biden warned Tuesday of a "very, very dangerous" situation without a Gaza ceasefire deal by Ramadan, adding that it was up to Hamas to accept a deal as talks continue in Cairo.
As the US military made its second airdrop of aid to Gaza, Biden also told ally Israel there were "no excuses" for failing to allow more aid into the Palestinian enclave where the UN warns famine is looming.
Biden's comments came as US frustration grows both with Israel over Gaza's aid needs and spiraling civilian death toll, but also with Hamas for stalling on conditions including the release of hostages.
"It's in the hands of Hamas right now," Biden, 81, told reporters as he flew back to the White House from the Camp David presidential retreat in the hills of Maryland.
"The Israelis have been cooperating, the offer (of a ceasefire) is rational. We'll know in a couple of days. But we need the ceasefire."
He added: "There's got to be a ceasefire because Ramadan -- if we get into circumstances where this continues to Ramadan, Israel and Jerusalem could be very, very dangerous."
Ramadan will start on March 10 or 11, depending on the lunar calendar.
Biden did not elaborate, but the United States last week urged Israel to allow Muslims to worship at the flashpoint Al-Aqsa mosque compound in Jerusalem during Ramadan, after a far-right minister proposed barring Palestinians from the occupied West Bank.
Democrat Biden faces acute political pressure in an election year over his support for Israel amid Gaza's soaring civilian death toll, which the health ministry there has put at 30,631, mostly women and children.
Israel vowed to eliminate Hamas after its unprecedented October 7 attack on southern Israel that resulted in the deaths of around 1,160 people, according to an AFP tally of official figures
US Secretary of State Antony Blinken separately called on Hamas to accept an "immediate ceasefire" with Israel as the militants met Qatari and Egyptian mediators in Cairo.
"It is on Hamas to make decisions about whether it is prepared to engage in that ceasefire," he said as he met the Qatari prime minister in Washington.
While Washington publicly put the onus on Hamas to agree a ceasefire, it has become increasingly frustrated with Israeli Prime Minister Benjamin Netanyahu's refusal to rein in the offensive or let in aid.
"I'm working with them very hard," Biden, who is seeking reelection told reporters. "We must get more aid into Gaza. There's no excuses, none."
US cargo planes airdropped more than 36,000 meals to Gaza Tuesday in a joint operation with Jordan, the US military said.
It is the second such operation since Biden gave the order last week in the wake of a horrific incident in which more than 100 people were killed in chaotic scenes around a convoy of aid trucks in Gaza City.
Biden also brushed off suggestions of tensions with Netanyahu, after Benny Gantz, one of Netanyahu's rivals in the Israeli war cabinet, visited the White House on Monday for talks with Vice President Kamala Harris.
On Tuesday former military chief Gantz met US Defense Secretary Lloyd Austin at the Pentagon and Blinken at the State Department.
Biden said his relationship with Netanyahu was "like it's always been."
Democrat Biden and rightwinger Netanyahu have often been at odds during the four decades in which their political paths have crossed, but Biden has stuck by Israel during its war with Hamas.
