United Nations officials say five tons of bombs are missing from a storage site in the Gaza Strip.
U.N. spokesman Richard Miron said Tuesday that the explosives were under Hamas police guard when they disappeared. Miron said the three one-ton and eight quarter-ton bombs were extremely dangerous and needed to be disposed of in a safe manner.
Hamas officials did not immediately comment, but an Israeli military official, Peter Lerner, said it was likely the Palestinian militant group stole the explosives.
A U.N. bomb disposal team has been in Gaza for the last three weeks, working on collecting unexploded munitions dropped during Israel's offensive in the Palestinian territory.
Separately Tuesday, the U.N. aid agency for Palestinians (UNRWA) announced a $345-million recovery fund for Gazans to rebuild after the three-week conflict with Israel. UNRWA'S Commissioner-General, Karen Abu Zayed, said about half of that money already has been collected.
Palestinian officials say Israeli military aircraft struck smuggling tunnels near the Gaza-Egypt border and a former security compound near the town of Khan Younis early Wednesday. An Israeli military official confirmed the airstrikes, which reportedly caused no casualties.
Both Israel and Hamas declared unilateral cease-fires last month, and Egypt continues to mediate efforts to forge a durable truce.
Israel's security cabinet is due to meet Wednesday to discuss its latest step.
Hamas wants Israel to open all of Gaza's border crossings, including one to Egypt. Israeli officials said they will not consider the demand until Hamas frees Israeli soldier Gilad Shalit, captured in Gaza more than two years ago.
Hamas says Shalit's freedom must be negotiated separately. It is demanding the release of hundreds of prisoners - including militants responsible for suicide attacks - in exchange for the captured soldier.
Some information for this report was provided byAP and Reuters.