Indirect ceasefire talks between Israel and Palestinian militant group Hamas in Doha ended in deadlock last week with the sides trading blame for the impasse and gaps remaining over issues including the extent of Israeli forces' withdrawal.
Witkoff, who will meet Israeli Prime Minister Benjamin Netanyahu, arrives on Thursday as Israel faces mounting international pressure over Gaza, with Canada the latest Western power to say it will recognise a Palestinian state.
Israel on Wednesday sent a response to Hamas's latest amendments to a US proposal that would see a 60-day truce and the release of hostages in exchange for Palestinian prisoners, a source familiar with the details said.
There was no immediate comment from Hamas.
Gaza medical officials said at least 23 people were reported killed by Israeli fire across the enclave, including 12 people among crowds who had gathered to receive aid around the Netzarim corridor, an area held by Israeli troops in central Gaza.
The Israeli military said it was looking into the report.
Since the war began, the Gaza health ministry has recorded 154 deaths from starvation and malnutrition, most of them in recent weeks, including at least 89 children.
Facing mounting international outrage over images of starving children, Israel said on Sunday it would halt military operations for 10 hours a day in parts of Gaza and designate secure routes for convoys delivering food and medicine.
The UN Office for the Co-ordination of Humanitarian Affairs said on Wednesday the United Nations and its partners had been able to bring more food into Gaza in the first two days of pauses, but the volume was "still far from enough".
Even with more aid running through Gaza, residents face peril from Israeli forces and Palestinian looters when trying to reach the supplies.
"I have tried several times to grab a sack of flour," one man from Deir Al-Balah told Reuters, asking not to be identified.
"The only time I managed to do so, someone with a knife froze me in the street and took it away, threatening to stab me
With the number of Palestinians killed in almost two years of war passing 60,000 this week, pressure has been mounting in Gaza on Hamas to reach a ceasefire deal with Israel.
In Israel, protests were expected in Tel Aviv and Jerusalem, calling on the government to end the war.
Netanyahu, whose ruling coalition includes two parties who want to conquer Gaza and re-establish Jewish settlements there, has said he will not end the war until Hamas no longer rules the enclave and lays down its arms. Hamas has rejected calls to disarm.
Qatar and Egypt, who are mediating the ceasefire efforts, backed a declaration on Tuesday by France and Saudi Arabia which outlined steps for a two-state solution to the Israeli-Palestinian conflict.
The declaration says Hamas "must end its rule in Gaza and hand over its weapons to the Palestinian Authority", which is led by its rivals and based in the Israeli-occupied West Bank.
Israel has rejected the Palestinian Authority gaining control of Gaza.
Israel has denounced declarations by France, Britain and Canada since last week that they might recognise a Palestinian state, which Israel says amounts to rewarding Hamas for its October 7, 2023, attack on Israeli territory.
That attack, when fighters killed 1200 people took 251 hostages back to Gaza, precipitated the war.
