U.S. officials say both Hamas and Israel are making concessions toward securing a deal, but tempered optimism with differences remaining on key issues.

U.S. and Arab mediators are working round-the-clock to hammer out a ceasefire deal between Israel and Hamas, sources close to the talks said, while in the Gaza Strip medics said Israeli strikes had killed 13 Palestinians on Thursday.

Israeli officials say a ceasefire in Gaza is a more realistic prospect than at any time in the past year, suggesting a long-awaited deal to free hostages and boost aid to the beleaguered territory could be close.

Israel and Hamas are closing in on an agreement to end more than 14 months of war. But so far, the sides remain unable to seal the deal.

The United States, joined by Arab mediators, sought to conclude an agreement between Israel and Hamas to halt the 14-month-old war in the Gaza Strip, where medics said Israeli strikes killed at least 20 Palestinians on Wednesday.

A leading Israeli newspaper, citing unnamed soldiers serving in Gaza, described indiscriminate killings of Palestinian civilians in the territory's Netzarim Corridor, prompting a firm rejection Friday from the military.