Monday’s exchange would bring to 51 the number of Israeli hostages freed since the four-day truce took effect Friday. Hamas has another 20 to 40 Israeli hostages it could release in the coming days.

That could potentially prolong the temporary cease-fire through Saturday morning because under the terms of the agreement brokered by Qatar it is extended by a day for every 10 additional hostages released by Hamas, limited to 10 days in total.

Hamas said in a statement late Sunday that it was hoping an extension would be possible with the aim of increasing the number of Palestinian prisoners freed from the 117 Israel has handed back thus far.

The announcement appeared to be the group’s first formal expression of a wish to keep the truce going beyond its official expiration at 7 a.m. local time Tuesday.

Israeli Prime Minister Benjamin Netanyahu, on a visit to Gaza on Sunday to meet with Israel Defense Forces — the first trip inside the occupied territory by an Israeli leader since 2005 — signaled that an extension was a possibility if Hamas continued to free hostages.

But he also talked tough, pledging that the war was not over until Hamas had been destroyed.

“We are continuing until the end, until victory. Nothing will stop us,” said Netanyahu, adding that he had told U.S. President Joe Biden in a phone call that the military offensive in Gaza would resume with full force once any extension came to an end.

Biden pledged his administration would do everything it could to see the truce extended so that more hostages could be freed and more badly needed humanitarian aid could be brought into Gaza for civilians.

He said he would remain personally engaged with Netanyahu to ensure the truce agreement was implemented in full, as well as working to get it extended.

Biden stressed that the deal was “structured so that it can be extended to keep building on these results.

“That’s our goal: to keep this pause going beyond tomorrow.”

Expectations were qualified by U.S. National Security Adviser Jake Sullivan who said on U.S. television Sunday that while the pause in the fighting could be extended one, two, three or “even more” days, it was up to Hamas.

“If the pause stops, the responsibility for that rests on the shoulders of Hamas, not on the shoulders of Israel,” said Sullivan who acknowledged the halt in the fighting had given Hamas the opportunity to refit and retool and exploit its achievements on social media.

Qatari officials also sought to temper expectations of a longer pause, warning that because hostages had been abducted by a number of different groups, Hamas did not know where they all were, making the task of finding the dozens needed for the extension problematic.

Prime Minister Sheikh Mohammed bin Abdulrahman Al Thani said it was understood at least 40 of the women and children held in Gaza were being held by groups other than Hamas.

“If they get additional women and children, there will be an extension. We don’t yet have any clear information how many they can find because one of the purposes [of the pause] is they will have time to search for the rest of the missing people.”