The reasons for rejection are often “very vague, and they are conveyed informally. Sometimes they were very unreasonable,” said Merkley, a Democrat from Oregon.

The two senators said they saw a warehouse in Rafah filled with material that had been rejected in inspection. It included oxygen cylinders, gas-powered generators, tents and medical kits used in delivering babies.

Aid workers told the senators the tents were refused because they included metal poles, and the medical kits because they included scalpels. Most solar-powered equipment appears to be barred — though it is vital in Gaza, where central electricity has collapsed and fuel for generators is in short supply.