Speaking to reporters on the sidelines of a meeting of G7 leaders in southern Italy, Sullivan said the world should encourage the Palestinian militant group to accept the proposal and avoid stalemate.

Sullivan said Israel is standing behind a ceasefire proposal for the eight-month-old war in the Gaza Strip, and the goal is to bridge gaps with Hamas and get to a deal soon.

Hamas has welcomed the ceasefire proposal, but insists any agreement must secure an end to the war, a demand Israel still rejects. Israel described Hamas's response to the new US peace proposal as total rejection. 

Since a brief week-long truce in November, repeated attempts to arrange a ceasefire have failed, with Hamas insisting on a permanent end to the war and full Israeli withdrawal from Gaza.

Sullivan said Hamas had submitted an amended proposal with some minor changes that could be worked out, as well as others that were not in line with what Biden had laid out or that had been embraced by the UN Security Council.

"Our goal is to figure out how we bridge the remaining gaps and get to a deal," he said, adding that discussions would continue with Qatar and Egypt, who, in turn, would work with Hamas to reach agreement as quickly as possible.

Sullivan stressed that Israel was standing behind the ceasefire proposal Biden outlined in a May 31 speech, adding that he had heard no Israeli leader challenge the deal.

Hamas precipitated the war when militants from Israeli-blockaded Gaza stormed into southern Israel in a lightning strike last Oct. 7, killing about 1,200 people and taking over 250 hostages back to the enclave, according to Israeli tallies.

Israel's invasion and bombardment of Gaza since then has killed at least 37,000 people, according to the territory's health ministry. Thousands more are feared dead and buried under rubble, with most of the population of 2.3 million displaced.

Biden was expected to update G7 leaders on the ceasefire negotiations and how their countries could support the process, Sullivan said, underscoring the broader implications for increasing tension between Israel and Lebanon.

Biden would discuss "the increasing intensity and scope of the strikes by Hezbollah deeper into Israel, and including into civilian areas," Sullivan said, adding that a ceasefire in Gaza would help bring calm to that region as well.

G7 leaders would also compare notes on what he called "the continuing threat posed by Iran, both with respect to its support for proxy forces, and with respect to the Iranian nuclear program, where we continue to have grave concerns."