The Palestinian militant group Hamas launched an unprecedented attack on Israel on 7 October, killing more than 1,400 people and taking more than 200 hostage.
What is Hamas
Palestinian health officials say more than 4,000 people have been killed in Gaza since Israel launched retaliatory air strikes, and a ground offensive is expected.
What has been happening in the Gaza Strip?
The first trucks carrying aid into Gaza crossed the border from Egypt on Saturday following days of negotiations.
Israel agreed to allow around 20 trucks carrying food, water and medicine into Gaza through the Rafah border crossing. It was not immediately clear how long the crossing would stay open for.
It comes after the UN's agency for Palestinian refugees warned that time was running out to get aid into the Gaza Strip.
UNRWA said access to clean water was severely limited and “concerns over dehydration and waterborne diseases are high”.
Israel had said it would not end the “siege” until Hamas released hostages. On Friday, Hamas released two US hostages, the first captives released since the gunmen raided Israel two weeks ago.
Gaza's Hamas-run government said 18 Christian Palestinians were killed in an explosion within the compound of the Saint Porphyrius Church in Gaza City on Thursday night. The BBC has not been able to verify this figure.
Israel said its jets were targeting a Hamas launch site for rockets and mortars and that a wall of the church was damaged.
Palestinian officials said at least 471 people were killed by an explosion at the Al-Ahli Arab hospital in Gaza City on 17 October. The Israel Defense Forces (IDF) said this number has been deliberately inflated, but has not released its own assessment of how many died.
Hamas blames an Israeli air strike, but the Israeli military said the blast was caused by a failed rocket launch by Palestinian Islamic Jihad (PIJ) and point to the absence of a large crater or blast damage to adjacent buildings. PIJ has denied responsibility.
Will Israel invade Gaza?
Israel's stated goal is to destroy Hamas.
It also wants to rescue the hostages seized when Hamas attacked Israel. It now believes 200 people are being held in Gaza.
Israel has massed tens of thousands of soldiers on its borders with Gaza, along with tanks and artillery. It has activated some 300,000 reservists alongside its standing force of 160,000.
The Israeli military has prepared for an offensive by dropping bombs on Gaza and targeting Hamas commanders and its control centres.
Hamas is thought to have about 25,000 people in its military arm.
One of Israel's main targets is expected to be Hamas's vast labyrinth of underground tunnels beneath Gaza, which contain bunkers for leaders and command and control centres. It is thought some of the hostages could be held in the tunnels.
Hamas has previously claimed the tunnels stretch for 500km (310 miles). Many have entrances hidden within houses, mosques, schools and other public buildings.
Israel's troops are likely to avoid going into tunnels unless they have to, instead using explosives to destroy them.
It is thought that Hamas will lay booby traps and improvised explosive devices at entry points and along narrow streets.
A major challenge for the Israeli troops will be close-quarters fighting in densely populated urban areas.
Israel believes they has about 30,000 fighters, with weapons including automatic rifles, rocket-propelled grenades and anti-tank missiles.
