The toll of the two-week fighting between Israel and the Islamist Hamas group in Gaza topped 500 on Monday.

The UN Security Council has deplored the mounting violence and appealed for an immediate ceasefire.

Here are five things about the Israel-Gaza conflict.

1. History of the Gaza conflict

Israelis and Arabs have been fighting over Gaza on and off, for decades. It is part of the wider Arab-Israeli conflict.

After World War II and the Holocaust in which six million Jewish people were killed, more Jewish people wanted their own country.

They were given a large part of Palestine, which they considered their traditional home but the Arabs who already lived there and in neighbouring countries felt that was unfair and did not accept the new country.

In 1948, the two sides went to war. When it ended, Gaza was controlled by Egypt and another area, the West Bank, by Jordan. They contained thousands of Palestinians who fled what was now the new Jewish home, Israel.

But in 1967, after another war, Israel occupied these Palestinian areas and Israeli troops stayed there for years. Israelis hoped they might exchange the land they won for Arab countries recognising Israel's right to exist and an end to the fighting.

Israel finally left Gaza in 2005 but soon after, a group called Hamas won elections and took control there. Much of the world calls Hamas a terrorist organisation. It refuses to recognise Israel as a country and wants Palestinians to be able to return to their old home - and will use violence to achieve its aims.

Since then, Israel has held Gaza under a blockade, which means it controls its borders and limits who can get in and out.

2. What is Gaza and who controls it?

The Gaza Strip is an area about half the size of Singapore on the border with Egypt up against the Mediterranean Sea.

Technically part of the Palestinian Authority, it has been governed since 2007 by the militant group Hamas. With 1.8 million people living in just 139 square miles (360 sq km), Gaza is one of the most densely populated places on earth.

Hamas, which rejects the existence of Israel, recently agreed to form a unity government with the other main Palestinian political faction, Fatah. The new Palestinian Unity Government recognises the State of Israel. But the outbreak of current hostilities pitting Hamas against Israel has left the Fatah-controlled Palestinian Authority on the sidelines.

3. What sparked this latest wave of violence?

While rocket attacks from Gaza and Israeli military incursions in the West Bank are regular occurrences, last month's abduction of three Israeli teens in the West Bank have brought the tensions to a fever pitch.

When the bodies of Eyal Yifrach, Gilad Shaar and Naftali Frankel were found on June 30, Israel was grief-stricken. The Israeli government blamed Hamas, which denied responsibility but praised the abductions.

Israel carried out arrests and demolished homes of the suspects in the West Bank, and launched airstrikes against targets in Gaza that are used to lob rockets into Israel.

Palestinians stepped up rocket attacks and clashed with Israeli troops.

The mood darkened further when a Palestinian teenager was abducted and killed in Jerusalem in what police say could be a revenge killing. The news sparked clashes between protesting Palestinian youths and Israeli security forces in Jerusalem.

The attacks quickly escalated. Hamas and Palestinian Islamic Jihad have fired rockets with a reach that Israel had not previously seen, with air raid sirens going off as far away as Jerusalem, Tel Aviv and Haifa.

According to the Israeli Defense Forces, Israel has hit more than 1,872 sites in Gaza with either air strikes or naval bombardment.

4. Who are the key players?

Hamas controls the Gaza Strip and is considered a terrorist group by Israel and the United States. But while there is no Israeli military presence inside Gaza anymore, the effective control of Gaza's sea, air and borders is under Israeli control.

The Israeli Defense Forces (IDF) are the military arm of Israel and are well armed and exceptionally large given Israel's population. Most Israeli residents must go through compulsory military service and are automatically enrolled in the IDF's reserve forces.

Benjamin Netanyahu is the prime minister of Israel. After the Israeli teens were found dead, he said they were victims of "terrorists" and "human animals." When the Palestinian teen was found murdered, he telephoned the boy's father and said the murder was "abhorrent." Three Israelis have been indicted for the murder.

5. What's next?

The current conflict comes after almost two years of relative calm between Israel and the Palestinians and just months after the latest round of peace talks collapsed.

Unfortunately, there has been no sign that the conflict has reached its peak.

The Israeli military still believes that it has more of its mission to complete.

Hamas fighters may be emboldened by their ability to inflict pain on the Israeli forces, and they too may not want an immediate halt.

But the fact that the battle has moved into a heavily-populated urban area with reports in some cases of house-to-house fighting means that the civilian death toll will rise markedly.

With it will come added pressure from outside to end the operation once and for all, wrote BBC defence correspondent Jonathan Marcus.

The only way to put a stop to the regular outbreaks of violence is to start by securing a ceasefire and then looking for a long-term solution, said Martin Indyk, a diplomat with a long history of working in the region.

What a ceasefire requires above all, "is for Hamas to decide that it is in its interest to stop firing those rockets," he said.

Sources: BBC, CNN, Deutsche Welle, ABC News, CBS News

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