Indirect negotiations mediated by Qatar, Egypt and the United States have taken place in Doha in recent days, rekindling hope for an agreement between the two warring parties that has so far proven elusive.
On Wednesday, both sides accused the other of throwing up roadblocks, while Israeli President Isaac Herzog urged the country's leadership to move towards a deal.
"The hostages are in clear and immediate danger", Herzog, whose role is largely symbolic, said at an event marking the start of the Jewish festival of Hanukkah.
He called on "our leadership to act with all its power... to bring about a deal".
Fighting meanwhile raged on in the Gaza Strip, were rescuers said Israeli strikes on Wednesday killed at least 20 people.
Palestinian militant group Hamas, whose October 7, 2023 attack triggered the war, said in a statement that "the ceasefire and prisoner exchange negotiations are continuing... in a serious manner."
But, it added, Israel "has set new conditions" which have "delayed reaching an agreement".
Israel swiftly refuted the accusations, saying it was Hamas that was creating "new obstacles" to an agreement.
Efforts to strike a deal in numerous rounds of indirect talks have repeatedly failed over key stumbling blocks.
'Don't wait'
Hamas said the latest Israeli demands concern troop withdrawal, the terms of the proposed ceasefire and the potential release of prisoners held in Israeli jails, as well as "the return of displaced people" to their homes in Gaza.
It did not specify what the Israeli conditions were.
A statement from the office of Prime Minister Benjamin Netanyahu hit back, saying that "Hamas is once again lying, reneging on understandings already reached, and continuing to create new obstacles in the negotiations."
Just days ago, both sides had reported progress.
Netanyahu on Monday told a parliament session that there had been "some progress" in the talks, two days after Hamas and other Palestinian groups said a ceasefire agreement was "closer than ever".
In Israel, critics of Netanyahu including relatives of some of the dozens of hostages still in captivity in Gaza have accused him of stalling.
On Wednesday, a group of family members of Gaza hostages urged Netanyahu to secure a deal to bring their loved ones homes.
"It's time to bring them back, Netanyahu. It's up to you," said Sharon Sharabi, whose two brothers were abducted during the Hamas attack. One of them has died in captivity, according to the Israeli military.
"It's about time, don't wait," said Sharabi, reading out a statement at Tel Aviv's Hostages Square.
Israel and Hamas have agreed just one truce in more than 14 months of war.
The late 2023 one-week pause saw 80 Israeli hostages freed in exchange for 240 Palestinians detained by Israel, with 25 other captives, mostly Thai farm workers, also released.
Strikes
A primary bone of contention in negotiations since then has been the establishment of a lasting ceasefire.
Another unresolved issue has been Gaza's post-war governance, which remains highly contentious including within the divided Palestinian leadership.
Israel has repeatedly said it would not allow Hamas, which has ruled Gaza since 2007, to run the tiny coastal territory ever again.
In an interview with The Wall Street Journal last week, Netanyahu said: "I'm not going to agree to end the war before we remove Hamas."
Netanyahu has also said he would not agree to a complete withdrawal of troops from Gaza, and on Wednesday his defence minister, Israel Katz, said security matters in the Palestinian territory "will remain in the hands of the IDF", the Israeli military.
On the ground, Gaza's civil defence agency said at least 20 people were killed in Israeli strikes on Wednesday.
Four people including a child were killed in a strike that hit tents of displaced people in Gaza City, said civil defence spokesman Mahmud Bassal, adding that 25 others were wounded.
The Israeli military earlier said its forces had targeted a militant in a strike on Gaza City.
Israel's military campaign, launched in response to Hamas's unprecedented attack, has killed at least 45,361 people in Gaza, a majority of them civilians, according to figures from the Hamas-run territory's health ministry that the UN considers reliable.
The October 7 attack last year resulted in 1,208 deaths on the Israeli side, mostly civilians, according to an AFP tally of Israeli official figures.
Militants also seized 251 hostages, 96 of whom remain in Gaza including 34 the Israeli military says are dead.
