What is Hamas? What you need to know about the militant group that rules the Gaza Strip

Hamas launched a devastating and coordinated land, sea and air assault on Israel over the weekend, sparking chaos in the region and thrusting the nationalist movement firmly into the global spotlight.

The militant Palestinian group orchestrated an unprecedented attack on Israel on Saturday, killing many hundreds of people and injuring thousands more. Hamas' fighters have also taken more than 100 Israeli civilians, soldiers and foreign nationals hostage.

The attack marked the deadliest assault the country has suffered in generations and led Israeli Prime Minister Benjamin Netanyahu to declare that his country is at war.

Israel's counteroffensive against Hamas has seen its military conduct a barrage of airstrikes across the enclosed territory of the Gaza Strip, also killing many hundreds of people.

Israel is mobilizing a record 300,000 reservists and imposed a "complete siege" on the Gaza Strip, seeking to stop the supply of electricity, food, water and fuel to the already blockaded population of roughly 2.3 million people. It says it has now secured control of the Gaza-Israel border.

The Palestinian Health Ministry said Tuesday morning that 770 people have been killed in Gaza, and 4,000 injured. The Israeli Defense Forces said that over 900 Israelis have been killed, and over 2,700 injured.

This brings the total death toll as a result of the conflict so far to over 1,600.

The violence raises questions about the history, motivations and future of Hamas, a group that has been designated a terrorist organization by the U.S., Japan, Australia, Israel, the European Union and many other countries — although some only apply this label to its military wing.

What is Hamas?

Founded in 1987 and led by Ismail Haniyeh, Hamas is an acronym for Harakat al-Muqawama al-Islamiya, or the "Islamic Resistance Movement."

It is dedicated to the establishment of an independent Islamic state in historical Palestine and has controlled the Gaza Strip — one of two Palestinian territories, along with the West Bank — since 2007. The United Nations classifies Israel as an occupier state over the Palestinian territories, whose occupations and annexations following the 1967 Six-Day War remain in violation of international law.

Hamas is one of two major political forces in the Palestinian territories, the other being Fatah, a rival group previously known as the Palestinian National Liberation Movement. Fatah retains control of the Palestinian National Authority in the Israeli-occupied West Bank.

A power struggle emerged between Hamas and Fatah shortly after the former won the 2006 Gaza Strip elections which took place a year after Israel withdrew from the territory. Hamas' fighters seized Fatah's headquarters by force to claim control of the strip and the group has since maintained political control of the area.

The military wing of Hamas is known as the al Qassem Brigades, the largest and best-equipped military group operating within Gaza.

Since 2007, Israel has imposed an air, land and sea blockade on the Gaza Strip, saying the move was necessary to prevent Hamas attacks on the country. The United Nations and international human rights groups have condemned the blockade, and have described Gaza as the "the world's largest open-air prison." Residents of Gaza are surrounded by concrete walls and barbed wire fences, unable to leave the territory without Israeli-approved permits.

Between 2008 and 2023, Israeli airstrikes killed 6,407 Palestinians in the occupied territories, 5,360 of whom were in Gaza, according to the U.N. Israel suffered 308 fatalities in that time period. Israel says its strikes targeted Hamas operatives, though they drew condemnation from the U.N. and other groups over reported high civilian casualty counts.

Half of Gaza's population is under the age of 19 but faces dire economic prospects, as 16 years of Israel's blockade and a ban on imports and exports have crippled the economy. The unemployment rate in Gaza is above 40%, more than 65% of the population is under the poverty line, and 63% of Gazans are deemed food insecure, according to the U.N.

On Tuesday, the U.N. Relief and Works Agency said that conditions in the Gaza Strip remain "difficult" as heavy airstrikes continue, with some shelters overcrowded. It comes shortly after Israel imposed a complete siege on the already impoverished enclave, an order that threatens to exacerbate the situation.

"I am deeply distressed by today's announcement that Israel will initiate a complete siege of the Gaza Strip. Nothing allowed in, no electricity, food or fuel. The humanitarian situation was extremely dire before these hostilities. Now, it will only deteriorate exponentially," U.N. Secretary-General Antonio Guterres said Monday.

Basim Naim, head of international relations for Hamas in Gaza, told BBC's "World at One" radio show on Monday that civilians in the Gaza Strip had been living in a "suffocating siege" for around 17 years, one that "unfortunately [has been] supported by the international community."

"All this together has accumulated a huge anger by the Palestinians, and we have always warned the diplomats and the politicians we have met that this situation is unsustainable," Naim said. "People under occupation has always the right to resist by all available means, including armed resistance."

Israel's Netanyahu has pledged to take "mighty vengeance" for what he called Hamas' "cruel and wicked war."

Prior to Hamas' surprise attack on Oct. 7, fighting between Hamas and Israel was at its deadliest in 2021, when, following growing tensions between Palestinians and Israelis in Jerusalem, the militant group fired rockets into Israel.

Hamas has received international backing from countries such as Turkey and Qatar, while Iran is known to be one of the group's biggest benefactors.

Iran's top official Ayatollah Ali Khamenei said Tuesday that Tehran was not involved in Hamas' attack over the weekend. Khamenei praised, however, what he described as Israel's "irreparable" military and intelligence defeat.

"We kiss the foreheads and arms of resourceful and intelligent designers and Palestinian youth, but those who say that the recent saga is the work of non-Palestinians have miscalculated," he said in Google-translated comments carried by the Iranian state-owned Islamic Republic News Agency.

Iran has been sanctioned by the U.S. and is a long-standing regional rival of Israel.

— CNBC's Natasha Turak and Ruxandra Iordache contributed to this report.