Blinken toured a loading zone for the relief goods on the dusty outskirts of Amman before flying to Israel, where he said he would insist on further humanitarian access in talks on Wednesday.
Israel, under pressure from President Joe Biden, said in early April that it would allow aid deliveries through the Erez crossing into northern Gaza and allow docking at the Ashdod port just north of the blockaded territory.
But Israel called the moves temporary and did not give a timeframe, with Prime Minister Benjamin Netanyahu facing pushback by hard-right members of his government.
Blinken said the first convoy of trucks from Jordan, which includes supplies from US charities, was leaving for Erez crossing later Tuesday.
"It is real and important progress, but more still needs to be done," Blinken said.
"We have to make sure that our focus is not only on inputs, but on impact, and really measuring whether the aid that people need is actually getting to them in an effective way," he said.
Blinken said he also met in Jordan with a group of women who have escaped Gaza and "heard the suffering that they endured."
In the packed warehouse managed by the Jordan Hashemite Charitable Organization, sealed boxes bore the names of charities that funded them including Arab-American and US-based Islamic groups.
Inside were medical supplies and food staples such as cooking oil, rice and nuts.
A Jordanian official said the shipment would feed 100 to 150 families for around a week — a drop in the bucket in a territory where virtually the entire population of two million people has been displaced.
The United Nations has warned of famine, with the United States saying it has heard of deaths from malnutrition, after the relentless military campaign in response to the October 7 attack by Hamas on Israel, the deadliest in the country's history.
Biden, who has stood by Israel, warned that future support was at stake after an April 1 Israeli strike killed seven aid workers from World Central Kitchen, the charity founded by celebrity Spanish-American chef Jose Andres.
Asks of Israel
The Biden administration has also acted on its own including by building a temporary pier to bring in aid — an extraordinary step to deal with concerns about a friendly country and major recipient of US assistance.
Blinken said he hoped the pier would be ready in about a week. Cypriot President Nikos Christodoulides told reporters the United States had informed his government that the floating dock would be ready by Thursday.
Blinken, who will see Netanyahu on Wednesday, said he would press Israel to agree on a "clear affirmative list" of goods needed in Gaza so they are not subject to "arbitrary denials."
Aid workers and US lawmakers have charged that Israel has put aid deliveries through exhaustive, time-consuming checks and sometimes denied their entry entirely.
Blinken also acknowledged logistical issues in Gaza including a lack of drivers and effective distribution networks.
Israel has long criticized the UN agency for Palestinian refugees UNRWA and has ramped up pressure after accusing several staff members of participating in the October 7 attack.
The US Congress has forbidden any further assistance to UNRWA, whose supporters say it is the only institution that is able to distribute in Gaza.
Blinken met in Amman with the UN humanitarian and reconstruction coordinator for Gaza, Sigrid Kaag, and saluted the "extraordinary work" by the world body.
Working with Jordan
Blinken met separately with Jordan's King Abdullah II and Foreign Minister Ayman Safadi, including on a proposal backed by the United States for a temporary ceasefire and release of hostages.
Jordan's foreign ministry said Safadi spoke to Blinken on the need for a comprehensive plan toward Palestinian statehood.
Jordan, which has diplomatic relations with Israel and has a large Palestinian population, is especially sensitive to tensions in the Palestinian territories.
Earlier in April, Jordan shot down Iranian drones fired at Israel in response to a deadly air strike on the Iranian consulate in Syria.
Jordan, while working with the United States, has insisted it does not want to be caught in the middle of the conflict.
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