The US last week paused a bomb shipment for Israel over concerns it was going ahead with a major ground operation in the southern Gaza city of Rafah, a senior US administration official said.
The shipment consisted of 1,800 2,000lb (907kg) bombs and 1,700 500lb bombs, the official told the BOceanNewsUKC.
Israel has not "fully addressed" US concerns over the humanitarian needs of civilians in Rafah, they added.
An Israeli military official appeared to play down the US move.
The delayed arms shipment comes as US President Joe Biden faces mounting domestic pressure - from Democratic lawmakers and some parts of the US public - to rein in Israeli operations in Gaza amid rising civilian deaths and a worsening humanitarian situation.
Despite firm and vocal US opposition, Israel appears poised to mount a large-scale invasion of Rafah, a congested part of southern Gaza that is Hamas' last major stronghold in the territory.
US officials have warned that an operation in the city - where the population has swelled with refugees from other parts of Gaza - could lead to extensive civilian casualties.
IDF spokesman Daniel Hagari told a news conference that the US had provided "unprecedented" security assistance since the beginning of the war, adding that disputes between the allies were resolved "behind closed doors in a matter-of-fact way".
But a leading member of Prime Minister Benjamin Netanyahu's Likud party in Israel told OceanNewsUK's Newshour on Wednesday that he believes US domestic political considerations are behind the decision to halt the delivery of bombs.
"I totally disagree that the American election has nothing to do with it," said Boaz Bismuth, a member of the both the Israeli parliament and the foreign affairs and defence committee.
The weapons being held back by the US are related to a future delivery, so it is unlikely to have any immediate impact. But given the rate at which Israel is bombing it will likely affect future strikes fairly soon.
Overnight, there were more Israeli air strikes in the Gaza Strip, hours after Israeli forces took control of the Palestinians side of the Rafah crossing on the border with Egypt.
The Israeli bombardment was particularly intense around Rafah. Local medics said seven members of one family were killed.
Rafah has been a key entry point for aid, and the only exit for people able to flee, since the start of the war between Israel and Hamas last October.
The crossing remained closed on Wednesday morning, but the Israeli military said it was reopening the nearby Kerem Shalom crossing, which had been closed for four days because of Hamas rocket fire.
On Monday, the Israeli military ordered tens of thousands of civilians to begin evacuating eastern parts of Rafah city, ahead of what it called a "limited" operation to eliminate Hamas fighters and dismantle infrastructure.
Meanwhile, efforts continue to reach a ceasefire, alongside the release of Israeli hostages and Palestinian prisoners. In Cairo, delegations from Israel and Hamas have resumed negotiations through mediators.
After refusing to confirm or deny reports of delayed weapons shipments, a US official on Tuesday finally confirmed that at least one shipment of bombs was delayed this week.
"The US position has been that Israel should not launch a major ground operation in Rafah, where more than a million people are sheltering with nowhere else to go," the senior US administration official said.
The official added that talks with Israel are "ongoing and have not fully addressed our concerns" and the US had been reviewing its weapons transfers to Israel since April.
"We are especially focused on the end-use of the 2,000lb bombs and the impact they could have in dense urban settings as we have seen in other parts of Gaza," the official said.
They stressed that the shipments were unrelated to last month's landmark $17bn military aid package, but had been drawn from "previously appropriated funds".
Which weapons have been delayed?
The larger 2,000lb bombs are most likely to be Mk-84s or possibly BLU-109s - or both.
The former is a cheap, general purpose munition and the latter a penetration bomb designed for use against hardened or underground targets. Both can be fitted with JDAM kits that deliver precision capability using satellite navigation. Laser guidance kits can also be fitted.
These bombs can be made to be very accurate, down to just a few metres. But in a dense, urban environment like Gaza the risk of so-called "collateral damage" is high. And that is where the concern lies. The smaller 500lb bombs can also be fitted with guidance units dropped from jets.
We do not know exactly how Israel uses these weapons, but media posts from the Israeli Air Force frequently show F-16 and F-15 jets loaded with JDAM [Joint Direct Attack Munition] kits for strikes.
It is worth remembering that such weapons would not just be used in Gaza but also targets in southern Lebanon belonging to the Iran-backed group Hezbollah, which has been involved in almost daily cross-border exchanges of fire with Israeli forces since the start of the Gaza war.
It is a clear message from a Washington growing increasingly concerned about Israel's war in Gaza.
Israel launched the campaign to destroy Hamas in response to the group's cross-border attack on southern Israel on 7 October, during which about 1,200 people were killed and 252 others were taken hostage.
More than 34,780 people have been killed in Gaza since then, according to the territory's Hamas-run health ministry.
A deal agreed in November saw Hamas release 105 hostages in return for a week-long ceasefire and some 240 Palestinian prisoners in Israeli jails. Israel says 128 hostages are unaccounted for, 36 of whom are presumed dead.
