Egypt's campaign to shut down smuggling tunnels running under its border into the Gaza Strip threatens to throw thousands of Palestinians out of work.
The UN chief has called for an immediate ceasefire in the Gaza Strip and the US Secretary of State has headed to the region with a peace message.
There are theories among Israelis and Palestinians about what has propelled the two sides towards their second war in four years.
The Hamas government has barred much of Gaza's fruit imports from Israel, citing a need to cultivate local Palestinian agriculture.
Previous ceasefire deals after earlier rounds of fighting have often got off to a slow start with guns falling silent within a day or two.
Israel killed four Palestinian militants and wounded half a dozen others as it pursued air raids in Gaza for a third day on Saturday.
Militant groups in the Gaza Strip said on Thursday they had joined forces to step up attacks against Israel, possibly including suicide bombings.
Israel carried out air strikes on targets in the Gaza Strip on Friday after a rocket fired from the Palestinian territory exploded in Ashkelon.
Israeli troops and tanks left the Gaza Strip on Saturday, witnesses said, ending an incursion into the Hamas-ruled enclave.
Human rights groups and critics say some in the Islamist Hamas group, which rules Gaza, are exerting pressure to impose Islamic law on the public.