U.S. President Joe Biden's administration has been holding up certain Boeing-made arms shipments to Israel, four sources familiar with the matter told Reuters, in what two of them said was an apparent political message to the close U.S. ally.

The shipments, which have been delayed for at least two weeks, involved Boeing-made Joint Direct Attack Munitions, which convert dumb bombs into precision-guided ones, as well as Small Diameter Bombs.

The sources did not elaborate further, including on the political nature of the holdups. But they come at a time when Washington is publicly pressuring Israel to postpone its planned offensive in Rafah until after it has taken steps to avert civilian casualties.

The White House and Pentagon declined comment. The news of a delayed arms shipment was first reported by Axios over the weekend and Politico first reported on the types of arms delayed and the reasoning on Tuesday.

Without addressing whether there had been a holdup in arms shipments, White House press secretary Karine Jean-Pierre reaffirmed that Washington's commitment to Israel's security was "ironclad."

Still, when asked about the reports on the arms holdups, she added: "Two things could be true, in the sense of having those conversations, tough, direct conversations with our counterparts in Israel ... in making sure citizens lives are protected ... and getting that commitment."

The Pentagon said on Monday that there had not been a policy decision to withhold arms from Israel, America's closest Middle East ally.

Still, the delays appeared to be the first since Biden's administration offered its full support to Israel following Hamas' Oct. 7 attack, during which about 1,200 people were killed and about 250 others were abducted. About 133 of them are believed to remain in captivity in Gaza, according to Israeli tallies.

Israel's campaign to destroy Hamas has led to a seven-month-long military campaign that has killed a total of 34,789 Palestinians, most of them civilians, the Gaza Health Ministry said.

The conflict has also left many of Gaza's 2.3 million people on the brink of starvation and sparked protests in the U.S. demanding that universities and Biden withdraw support for Israel - including the provision of weaponry.

A senior Israeli official, speaking to Reuters on condition of anonymity, did not confirm any specific holdup in arms supplies but appeared to take the reports in stride: “As the prime minister has already said, if we have to fight with our fingernails, then we’ll do what we have to do.”