Hamas has softened its position in its latest Gaza cease-fire proposal but is sticking to a key demand that has been a major hurdle to a deal, according to two senior officials from countries involved in the negotiations.

That has dampened prospects for an imminent agreement, even as U.S. and Israeli officials have expressed optimism now that the talks are moving forward after weeks of deadlock.

Hamas presented a counterproposal on Wednesday. The two officials said that Hamas wanted international assurances that, once an initial truce kicks in, both sides will keep negotiating until they reach a final deal to end the war and free all of the hostages remaining in Gaza.

In effect, Hamas wants to ensure that it does not turn over many of the hostages only for Israel to restart the war, one of the officials said. Both senior officials spoke on the condition of anonymity because they were not authorized to speak publicly.

Israeli negotiators immediately rejected that demand, the two officials said. Israel wants the option to resume fighting if it deems it necessary. Without such leverage, Hamas might drag its feet, effectively obtaining an undeclared permanent cease-fire, one of the officials argued.

At the heart of the dispute is the question of the future of Gaza. Benjamin Netanyahu, the Israeli prime minister, has vowed to destroy Hamas and topple its rule in the Palestinian enclave. Hamas hopes that a permanent cease-fire will allow it to cling to power.