The Palestinian militant group Hamas pledged to uphold a new cease-fire with Israel on Wednesday, but its enforcement of that truce may be complicated by other armed factions that have increasingly challenged Hamas's authority in Gaza in recent years.
Hamas Islamists have dominated Gaza militarily since staging a 2007 coup that ousted secular Fatah forces loyal to Palestinian President Mahmoud Abbas. With an estimated 10,000 to 20,000 fighters in Gaza, Hamas far outnumbers any rival.
After fighting a three-week war with Israel from December 2008 to January 2009, Hamas agreed to an informal truce, ordering its fighters to refrain from rocket strikes on Israelis while cracking down on smaller groups who fired their own missiles across the border.
But that arrangement appeared to break down last month as Hamas militants increasingly joined those factions in launching rockets at Israel in response to what they said were acts of Israeli aggression.
Hamas had been under pressure from the other militants to prove its commitment to armed struggle against the Jewish state, whose existence they all reject.
Islamic Jihad: Gaza's No. 2
Gaza's second-strongest militant faction is Palestinian Islamic Jihad, which controls about 1,000 fighters. Like Hamas, PIJ was established by followers of Egypt's Muslim Brotherhood movement.
Unlike Hamas, PIJ does not manage social welfare programs for the poor and refuses to participate in Palestinian elections. Instead, it has focused on fighting Israel with occasional rocket strikes.
Salafists: A Growing Threat
The other main challenge to Hamas comes from Salafist militant groups that espouse a stricter version of Islam and support al-Qaida's goals of global jihad and a pan-Islamic caliphate.
Such groups have become increasingly active in Gaza since Hamas's 2007 takeover, attracting dozens to hundreds of members, including disaffected Hamas fighters.
In recent years, Salafist militants have accused Hamas of neglecting the struggle against Israel, and have tried to take the lead by carrying out their own sporadic rocket attacks.
Salafist groups also have complained about what they see as Hamas's failure to impose strict Islamic law in Gaza. Some have carried out attacks on sites they view as un-Islamic, including Internet cafes and Christian centers.
Responding to Challenges
One Salafist group, Jaish al-Islam, made headlines by abducting BBC reporter Alan Johnston in 2007 in a failed bid to secure the release of an al-Qaida cleric detained in Britain. Hamas later freed Johnston and punished the group for the abduction.
The leader of another group, Jund Ansar Allah, openly defied Hamas by declaring an Islamic emirate in Gaza in 2009. Hamas retaliated by attacking the Salafists, triggering a battle that killed at least 27 people.
It remains unclear whether Hamas's Gaza rivals will accept the latest Egyptian-mediated cease-fire and whether Hamas will crack down again if they resume their attacks on Israel.