An al Qaeda-aligned group abducted and killed a pro-Palestinian activist from Italy in the Gaza Strip, Hamas said on Friday.
Here are some key facts about what appears to be an increasingly assertive constellation of radical Islamists challenging Hamas's rule in the isolated Palestinian enclave.
* Vittorio Arrigoni's captors and presumed killers had issued a videotaped message under the "Jihadist Salafi" label demanding Hamas release their leader, Hesham al-Sa'eedni, who was arrested last month. At the time, Gazan sources identified Sa'eedni as a senior member of the Tawheed and Jihad group linked to al Qaeda. He is believed to be an Egyptian citizen.
* Other Islamist challengers to Hamas include:
Ansar al-Sunna (Followers of the Sunna), which carried out a lethal rocket attack on Israel last year and whose name had been used by, among others, al Qaeda-allied Sunni insurgents in Iraq;
Jund Ansar Allah (Warriors of God), who raided an Israeli border post -- on horseback;
Jaysh al-Islam (Army of Islam), closely linked to Gaza's powerful Doghmush clan, which worked with Hamas to capture Israeli soldier Gilad Shalit in 2006 but broke with it over the Doghmushes' four-month kidnap of a BBC journalist in 2007;
Jaysh al-Ummah (Army of the Nation), whose leader, Abu Hafs, was detained by Hamas;
Jaljalat (War Cry), which includes former Hamas members and is suspected of bombing several Internet cafes as part of its especially hard line against Palestinian "apostates."
Hamas has an ally in the long-established Palestinian Islamic Jihad faction, which has broad grassroots support and political prominence untypical of al Qaeda affiliates.
* The Salafists, whose diffuse network may be designed to evade Hamas crackdowns, share the goal of fighting Western powers and founding a purist Islamic state across the Middle East. Though Hamas echoes al Qaeda's calls to destroy Israel, its ambitions are framed within Palestinian nationalism and include political accommodation with secular rivals and a possible truce with the militarily superior Jewish state. Hamas has refrained from imposing sweeping Islamic law since taking over Gaza in 2007 and has condemned al Qaeda attacks abroad.
* Membership of the Salafist groups appears to number in the hundreds but with potentially thousands of supporters among Gaza's 1.5 million population. Hamas has some 25,000 men under arms and won a parliamentary election in 2006. There has been disillusion since then with its rule in Gaza and the Israeli-led embargo on Hamas which has ravaged the economy.
* Hamas has been publicly tolerant of Salafists, saying they are misguided and offering them "re-education." But in practice it has often tried to rein in Salafists intent on provoking Israel with cross-border attacks or violently undermining Hamas authority. In the bloodiest confrontation, Hamas forces stormed a mosque in the southern border town of Rafah in August 2009 after a Jund Ansar Allah preacher and leader, Abdel-Latif Moussa, publicly declared Gaza to be an Islamic emirate.
* Among Salafists' other complaints about Hamas are its tolerance of Gaza's 3,000-strong Christian community and the backing Hamas receives from Sunni Muslims' sectarian rivals in Shi'ite Iran. Most Palestinians, including Hamas members, are Sunnis. Salafists are also blamed for attacks on people and groups they see as defying religion, including Internet cafes.
(Reporting by Nidal Al-Mughrabi; Writing by Alastair Macdonald and Dan Williams)