Hamas militants have fired several rockets into Israel, rejecting an offer to extend a 12-hour humanitarian ceasefire.
Three mortars were fired from Gaza, hitting Israel in the Eshkol regional council shortly after 20:00 local time.
The Israeli government was ready to extend the 12-hour truce until midnight (10pm UK time) however, Hamas claims this was with the intention of preparing more military strikes.
Hamas official Sami Abu Zuhri sent a text message to reporters saying: "No agreement to extending the calm for an additional four hours."
During the original truce, Gazans had been recovering bodies and gathering supplies. Doctors in Gaza said 132 bodies were pulled from rubble during the ceasefire, taking the number of Palestinians killed in 19 days of violence to more than 1,000.
A senior Israeli official confirmed that the UN had requested a 24-hour extension to the ceasefire.
"At the first stage, the cabinet approved, in a phone vote, four more hours until midnight, in order to allow the cabinet to convene and discuss the UN's request," the official said.
"The IDF [Israel Defence Forces] maintains the humanitarian pause, during which, the IDF's activity to neutralise the [Hamas] tunnels will continue."
After the Hamas rockets were fired into Israel, the people of Gaza are now bracing themselves for Israeli strikes.
Meanwhile, as fighting recommences, world leaders are continuing their efforts to negotiate a wider ceasefire in Paris.
US Secretary of State John Kerry, who is in Paris for talks with British Foreign Secretary Philip Hammond and other counterparts from Europe, Turkey and Qatar, said he remains "confident progress can be made" on a seven-day truce that would "bring people together to create a more durable plan".
Mr Kerry told a news conference in Cairo a "fundamental framework" for peace was in place and that it would "ultimately succeed".
"The world is watching tragic moment after tragic moment unfold and is wondering when everybody is going to come to their senses," said Mr Kerry.
In London, anti-war protesters marched from the Israeli embassy to the Houses of Parliament.
Protests also took place in France and Germany.