Abdul-Latif Moussa was surrounded by militants in the mosque on Friday
The Palestinian Islamist militant group Jund Ansar Allah, or the Soldiers of the Followers of God, announced its presence in the Gaza Strip in June when three of its members were killed in a horseback raid on an Israeli border post.
It has criticised the rival Islamist group, Hamas, which controls the coastal territory, for failing to establish Islamic law and for abiding by the ceasefire called after the Israeli offensive ended in January.
On Friday, the leader of Jund Ansar Allah, Abdul-Latif Moussa, declared in a sermon at Rafah's Ibn-Taymiyah mosque that Gaza was now an "Islamic emirate". Hamas forces attacked later that day.
Moussa, a doctor and local cleric, was killed alongside 21 others in the ensuing battle. Hamas officials said he and an aide named Khaled Banat, a Syrian national of Palestinian origin also known as Abu Abdullah al-Muhajir, had blown themselves up using explosive vests.
Jund Ansar Allah was set up in southern Gaza in November 2008 as an armed jihadist group with strong Salafist religious credentials.
JUND ANSAR ALLAH
Name means Soldiers of the Followers of God
Member of Salafist movement, advocating return to the type of Islam practised at the time of the Prophet Muhammad
Wants to establish Islamic emirate throughout Middle East
Calls for strict enforcement of Sharia law, says Hamas is too liberal
Several hundred sympathisers in southern Gaza
Salafis call for a return to the political and moral practices of the first Muslims, in particular the "righteous ancestors", known as "Salaf al-Salih".
On its website, the group says it has vowed to God to "fight a jihad for his sake" until the "banner of unity is hoisted" and the Prophet Muhammad "is made victorious". It also considers Islamic law the sole source of legislation and any deviation from it apostasy.
The group also says it wants to unify the mujahidin, including Hamas and Islamic Jihad, and liberate Muslim prisoners from Israeli jails.
Operating initially in Rafah and Khan Younis, Jund Ansar Allah spread rapidly throughout Gaza and, until Friday's raid, claimed to have 500 members, including a number of foreign fighters.
It is said to have a military base in a former Israeli settlement, from which it carried out a number of minor attacks on Israeli forces during the first half of the year, according to its website.
On 8 June, however, the group came to public attention with a spectacular, if unsuccessful, raid on the Karni border crossing.
At least three of its fighters were shot dead by Israeli troops after 10 rode into battle on horses laden with large quantities of explosives.
Israeli officials said several of the men had been wearing explosive belts, and suspected they had been attempting to kidnap a soldier.
Hamas officials have also blamed the "outlaws" for the bombings of several internet cafes, seen as a source of immorality, and of a wedding party attended by relatives of the West Bank-based Fatah leader, Muhammad Dahlan.
The group came to public attention with a horseback raid on a border crossing
Fifty people were injured in the latter attack, for which Jund Ansar Allah has denied any responsibility. Fatah leaders blame Hamas.
Earlier this week, an unsuccessful attempt was apparently made by Hamas to detain the group's military commander, believed to be Abu Abdullah al-Muhajir.
Hamas security forces approached him as he was leaving a mosque in Rafah. According to a source close to Hamas, Muhajir and his bodyguards threatened to detonate explosive belts they were wearing, and escaped.
Then on Friday, Jund Ansar Allah announced on its website and jihadist forums its allegiance to the "Islamic emirate in the heart of Beit al-Maqdis (Jerusalem)".
The statement also declared that its leader was Abdul-Latif Moussa, also known as Abu al-Nur al-Maqdisi.
"The soldiers of tawhid [unification] will not rest... until all Muslim lands are liberated and until our imprisoned al-Aqsa [mosque] is purified from the desecration of the accursed Jews," it said.
The group also demanded that Hamas "cease its aggression against Salafis" and warned of a confrontation if security forces interferred.