What is happening in Israel and Gaza, and what is Hamas?

Hamas gunmen launched an unprecedented assault on Israel from the Gaza Strip on 7 October, killing more than 1,400 people and taking at least 240 hostages.

Since then, Israel has been carrying out retaliatory strikes on Gaza, in which more than 8,700 people have been killed, according to the Hamas-run health ministry.

Israel has also sent troops and tanks into the territory.

Israel’s Prime Minister, Benjamin Netanyahu, said on Monday that he had set “the clear goal of destroying Hamas’s military and governing capabilities”, as well as freeing the hostages.

He also rejected calls for a ceasefire, saying they were “calls for Israel to surrender to Hamas”.

The Israel Defense Forces (IDF) said on Wednesday that it had so far struck more than 11,000 “targets belonging to terrorist organisations” in Gaza.

On Tuesday, the IDF carried out an air strike on Jabalia refugee camp, in northern Gaza, which caused several residential buildings to collapse.

Gaza’s Hamas-run health ministry says at least 50 people were killed. A senior doctor at a nearby hospital told the BBC it had received 120 dead.

The IDF said the strike killed a senior Hamas military commander and a large number of Hamas fighters in “underground terror infrastructure” beneath the buildings. The underground infrastructure collapsed after the strike, it added.

Israel ground forces, meanwhile, continued to move forward from a number of directions, gradually closing in on some of the northern Gaza Strip’s most populated areas, including Jabalia.

The IDF has said15 of its soldiers were killed in battles inside Gaza on Tuesday, and that a total of 330 have been killed since 7 October.

On Sunday, eyewitnesses described heavy shelling around the Al-Quds Hospital in Gaza City, in which 14,000 people were thought to be sheltering.

The Palestinian Red Crescent said the Israeli military had told staff to evacuate, but that it was impossible to move the hundreds of patients who are being treated there.

The IDF has massed tens of thousands of soldiers, along with tanks and artillery, both along Gaza’s borders and within the territory. It has activated some 300,000 reservists alongside its standing force of 160,000.

Hamas is thought to have about 25,000 members in its military wing. It also has a network of underground tunnels across Gaza, connecting its command centres, which it has said stretch for 500km (310 miles).

The World Health Organization (WHO) has warned that a “public health catastrophe” is imminent in Gaza, where a third of hospitals are not functioning and the rest are barely working due to shortages of fuel and medical supplies.

An estimated 1.4 million people have moved southwards since the Israeli military ordered residents of northern Gaza to leave their homes for their own safety on 13 October.

The southern city of Khan Younis, normally home to 400,000 people, has seen its population increase to about 1.2 million since the latest conflict began.

Many families are sharing homes, or sleeping in tents. About 600,000 are being hosted by Unrwa, the UN agency for Palestinian refugees.

The UN has warned Gaza has only 5% of its normal daily water output, with infant deaths from dehydration “a growing threat”.

Unrwa said on Sunday that thousands of Gaza residents had broken into its distribution centres and warehouses “taking wheat flour and other basic survival items like hygiene supplies”.

Gaza normally receives 500 lorry loads of supplies a day, but only a fraction of that amount has been passing through the Rafah crossing with Egypt.

US President Joe Biden has told Israel that the flow of aid into Gaza needs to be considerably increased.

There have also been no shipments of fuel, which is needed to generate electricity for hospitals, shelters, bakeries, water treatment and pumping stations, as well as the sewerage system.

Israel has refused to allow deliveries of fuel because it says it could be used for military purposes by Hamas. It also said that Hamas has hundreds of thousands of litres of fuel that it is refusing to hand over to aid agencies.

The Rafah crossing opened for people on Wednesday for the first time since 7 October.

Dozens of seriously injured Palestinians and at least 320 foreign passport holders were allowed to leave Gaza for Egypt.

The UK Foreign Office said British nationals were expected to leave Gaza in stages over the coming days.

The Israeli military says at least 240 people are still being held in Gaza. These include 20 children and at least 10 people aged over 60. Soldiers were also taken.

The WHO says it is “gravely concerned” about the condition of hostages being held by Hamas – especially those who are children, elderly or in poor health.

It is calling for the immediate release of all the hostages.

It is thought Hamas may have captured the hostages to pressure Israel into freeing some or all of the estimated 5,100 Palestinians who were held in Israeli prisons at the start of the month.

On Monday, Hamas published a video showing three women held hostage in Gaza, one of whom called on Mr Netanyahu to agree to the Palestinian prisoners’ release in exchange for their freedom.

Mr Netanyahu condemned the video as “cruel psychological propaganda”.

Hamas has so far released four hostages, following mediation by Qatar and Egypt.

On 20 October, two American-Israeli hostages – mother and daughter Judith and Natalie Raanan – were freed. Four days later, two elderly Israeli women, Nurit Cooper and Yocheved Lifschitz, were released.

On Monday, Israel’s military said its soldier Pte Ori Megidish had been rescued during ground operations in Gaza on Sunday night.

Hamas is a Palestinian group which has ruled the Gaza Strip since 2007. The group is sworn to Israel’s destruction and wants to replace it with an Islamic state.

Hamas has fought several wars with Israel since it took power. It has fired – or allowed other groups to fire – thousands of rockets into Israel, and has carried out other deadly attacks.

In response, Israel has repeatedly attacked Hamas with air strikes. In 2008 and 2014, it also sent troops into Gaza.

Together with Egypt, Israel has blockaded the Gaza Strip since 2007 for what it describes as security reasons.

Hamas – or in some cases its military wing, the Izzedine al-Qassam Brigades – has been designated a terrorist group by Israel, the United States, the European Union and the UK, as well as other powers.

Iran backs the group, providing it with funding, weapons and training.

On 7 October, hundreds of Hamas gunmen crossed from the Gaza Strip into southern Israel by breaking through the heavily fortified perimeter fence, landing by sea, and using paragliders.

It was the most serious cross-border attack Israel has faced in more than a generation.

The gunmen killed 1,400 people, most of them civilians, in a series of raids on military posts, kibbutzim and a music festival, and took hostages back into Gaza.

Mr Netanyahu said after the attack that Israel was at war, and vowed that Hamas would “pay an unprecedented price”.

Given the significant resources of Israel’s security services, it was astounding that the attack by Hamas was not anticipated, the BBC’s security correspondent Frank Gardner says.

The attack came at a time of soaring Israeli-Palestinian tensions.

This year has been the deadliest on record for Palestinians who live in the Israeli-occupied West Bank, which could have motivated Hamas to strike Israel.

Hamas might also have been seeking to score a significant propaganda victory to boost its popularity among ordinary Palestinians.

The Gaza Strip is a 41km (25-mile) long and 10km-wide territory located between Israel, Egypt and the Mediterranean Sea.

Originally occupied by Egypt, Gaza was captured by Israel during the 1967 Six Day war.

Israel withdrew its troops and around 7,000 settlers from the territory in 2005.

It is home to 2.23 million people and has one of the highest population densities in the world.

Just over 75% of Gaza’s population – some 1.7 million people – are registered refugees or descendants of refugees, according to the UN. More than 500,000 of them live in eight crowded camps located across the Strip.

Israel controls the air space over Gaza and its shoreline, and has strictly controlled the movement of people and goods.

The West Bank and Gaza, which are known as the Palestinian territories, as well as East Jerusalem and Israel all formed part of a land known as Palestine from Roman times until the mid-20th Century.

These were also the lands of Jewish kingdoms in the Bible, and are seen by many Jews as their ancient homeland.

Israel was declared a state in 1948, though the land is still referred to as Palestine by those who do not recognise Israel’s right to exist.

Palestinians also use the name Palestine as an umbrella term for the West Bank, Gaza and East Jerusalem.

The Palestinian president is Mahmoud Abbas, also known as Abu Mazen. He is based in the West Bank, which is under Israeli occupation.

He has been the leader of the Palestinian Authority (PA) since 2005, and represents the Fatah political party, a bitter rival of Hamas.