An explosion from an Israeli strike in the northern Gaza Strip is pictured from the Israeli border with Gaza, early morning July 26, 2014, before a cease-fire takes effect. [Photo/Agencies]

A 12-hour humanitarian truce went into effect on Saturday after Israel and Palestinian militant groups in the Gaza Strip agreed to a U.N. request for a pause in fighting and efforts proceeded to secure a long-term ceasefire moved ahead.

Children under air strike in Gaza

The Gaza Health Ministry said 18 members of a single family were killed by Israeli tank shelling in the southern Gaza Strip shortly before the truce took effect at 8 a.m. (1 a.m. EDT). An Israeli military spokeswoman said she was checking the report.

Israel's military said it would hold fire for 12 hours, but would press on with its search for tunnels used by militants. A spokesman for the Islamist group Hamas, which dominates Gaza, said all Palestinian factions would abide by the brief truce.

Hundreds of Palestinians poured into the streets in the minutes after the truce took force, some headed on foot to their homes to inspect damage from the Israeli assaults and many lined up outside banks to withdraw cash and stock up on supplies.

Fighting had continued overnight as US Secretary of State John Kerry, on a visit to the region, spearheaded international efforts to end 19 days of conflict in which 883 Palestinians, many of them civilians, have been killed.

Gaza officials said five people were killed in Israeli air strikes in the night and militants fired a barrage of rockets out of Gaza, triggering sirens across much of southern and central Israel. No injuries were reported, with the Iron Dome interceptor system shooting down some of the projectiles.

Gaza Health Ministry spokesman Ashraf Al-Qidra said that 18 members of the Al-Najar family killed had been trapped inside their house in Khuzaa village east of Khan Younis since Thursday and that many others were wounded in Israeli tank shelling.

Israel said that two more of its soldiers were killed in Gaza, bringing the army death toll to 37, as troops battled militants in the north, east and south of Gaza - a tiny Mediterranean enclave that is home to 1.8 million Palestinians.

It also announced that a soldier unaccounted for after an ambush in Gaza six days ago was definitely dead, although his body had not been recovered. Hamas said on Sunday it had captured the man but did not release a photograph of him.

Three civilians have also been killed in Israel by rockets from Gaza - the kind of attack that surged last month amid Hamas's anger at a crackdown on its activists in the West Bank, prompting the July 8 launch of the Israeli offensive.