"We wait to see whether, in effect, they can take yes for an answer on the ceasefire and release of hostages," Blinken said late Friday.
"The reality in this moment is the only thing standing between the people of Gaza and a ceasefire is Hamas."
Noting that the militants "purport to represent" the Palestinian people, Blinken said: "If it is true, then taking the ceasefire should be a no-brainer."
"But maybe something else is going on, and we'll have a better picture of that in the coming days," he said.
Blinken pointed to difficulties negotiating with Hamas, which the United States considers a terrorist group and does not engage with directly and which Israel has vowed to eliminate.
"The leaders of Hamas that we're indirectly engaged with -- through the Qataris, through the Egyptians -- are, of course, living outside of Gaza," Blinken said.
"The ultimate decision-makers are the folks who are actually in Gaza itself with whom none of us have direct contact."
Blinken was addressing the McCain Institute's Sedona Forum in Arizona days after he met with Israeli Prime Minister Benjamin Netanyahu and other top leaders on his latest visit to the Middle East.
Ahead of his talks with Blinken, Netanyahu vowed to push ahead with an assault on the southern Gaza city of Rafah regardless of the outcome of truce negotiations.
US President Joe Biden's administration has repeatedly warned Israel against moving on Rafah, where an estimated 1.2 million Palestinians have taken shelter.
Blinken said that Israel, which counts on the United States for military and diplomatic support, has yet to present "a credible plan to genuinely protect the civilians who are in harm's way".
"Absent such a plan, we can't support a major military operation going into Rafah because the damage it would do is beyond what's acceptable," Blinken said.
Global criticism of the war's toll on civilians has mounted, as has pressure on the Biden administration.
The war broke out after Hamas's October 7 attack resulted in the deaths of more than 1,170 people, mostly civilians, according to an AFP tally of Israeli official figures.
The militants also took around 250 hostages, of whom Israel estimates 128 remain in Gaza, including 35 believed to be dead.
Israel's retaliatory campaign has killed at least 34,622 people in Gaza, mostly women and children, according to the Hamas-run territory's health ministry.
Saudis want progress 'as soon as possible'
Blinken on Monday held his latest meeting with Saudi Arabia's de facto ruler, Crown Prince Mohammed bin Salman, to discuss potential normalization with Israel.
"He's made it clear that he wants to do something on normalization, and he'd like to do it as soon as possible," but only if conditions are met, Blinken said.
Before Hamas's October 7 attacks, Netanyahu had seen growing Arab recognition of Israel as a key legacy and Saudi Arabia, the guardian of Islam's two holiest sites, would be the most coveted prize.
But Saudi Arabia has made clear it wants a pathway to a Palestinian state, a prospect long resisted by Netanyahu and adamantly opposed by his far-right allies.
"I believe that there can be a Palestinian state with necessary security guarantees for Israel," Blinken said.
"And to some extent, I think you'd have Israelis who would like to get to real separation. Well, that is one way to do it."
While in Saudi Arabia Blinken said that the United States was nearly ready with a set of security promises sought by the kingdom in return for normalization with Israel.
