The Palestinian group Hamas has launched a surprise attack from Gaza into Israel, in one of the most serious escalations in the Israel-Palestinian conflict in years.

What is Hamas?

- Hamas, or the Islamic Resistance Movement, was founded in 1987 during the first Palestinian Intifada, or uprising. It is backed by Shi'ite Iran and shares the Islamist ideology of the Muslim Brotherhood, which was established in Egypt in the 1920s.

- It has run the Gaza Strip since 2007, after a brief civil war with forces loyal to the Fatah movement led by President Mahmoud Abbas, who is based in the West Bank and also heads the Palestine Liberation Organization (PLO).

The Hamas takeover of Gaza followed its win in Palestinian parliamentary elections in 2006 – the last time they were held. Hamas accused Abbas of conspiring against it. Abbas described what happened as a coup.

Since then, there have been numerous rounds of conflict with Israel, often involving Hamas rocket attacks from Gaza into Israel and Israeli airstrikes and bombardment of Gaza.

- Hamas refuses to recognise the state of Israel and violently opposed the Oslo peace accords negotiated by Israel and the PLO in the mid-1990s.

- Hamas has an armed wing called the Izz el-Deen al-Qassam Brigades, which has sent gunmen and suicide bombers into Israel. Hamas characterizes its armed activities as resistance against Israeli occupation.

Its 1988 founding charter called for the destruction of Israel, although Hamas leaders have at times offered a long-term truce, or Hudna in Arabic, with Israel in return for a viable Palestinian state on all Palestinian territory occupied by Israel in the 1967 war. Israel regards this as a ruse.

- It is designated as a terrorist organisation by Israel, the United States, European Union, Canada, Egypt and Japan.

- Hamas is part of a regional alliance comprising Iran, Syria and the Shi'ite Islamist group Hezbollah in Lebanon, which all broadly oppose U.S. policy in the Middle East and Israel.

- While its power base is in Gaza, Hamas also has supporters across the Palestinian territories, and it has leaders spread across the Middle East in countries including Qatar.

(Compiled by Tom Perry; Editing by Ros Russell)