Explosions at two sensitive sites in the Gaza Strip [ID:nLU529969] have prompted speculation on Sunday that they were the work of al Qaeda-aligned radicals opposed to the Palestinian enclave's Islamist rulers Hamas.

Here are comments on key questions about the incidents:

WHO WAS BEHIND THE BOMBINGS?

No credible claim of responsibility has been made.

Since Hamas seized control of the Gaza Strip in June 2007 by routing secular forces loyal to Palestinian President Mahmoud Abbas, the Islamists have tended to blame occasional bombings and other attacks on Hamas targets on Abbas's Fatah party. This time, however, suspicion has fallen on fundamentalist Muslims, or Salafis, whose agenda of global jihad, or holy war, against the West is at odds with Hamas's nationalist goals.

Hamas forces attacked a mosque in Rafah on Aug. 14 [ID:nLF47066] after the leader of a group calling itself Jund Ansar Allah (Warriors of God) declared Islamic rule in the town on the border with Egypt. Up to 28 people, including the leader, were killed. That sparked warnings of a reaction [ID:nLI78639] and speculation that conflict with Salafis could both complicate and foster Hamas's contact with the West [ID:nLH515758].

WHO ARE THESE SALAFIS?

Click here [ID:nLH515758] for details of known groups.

Most share an agenda with al Qaeda and believe Hamas broke with Islam by taking part in the 2006 Palestinian parliamentary election -- an election which it won, sparking international sanctions. Since Hamas [ID:nLF53592] seized control of Gaza in 2007 from secular President Abbas, Salafis have criticised the Islamist movement for failing to implement Islamic law.

Though they may not have a clear hierarchical connection to al Qaeda, they admire its leaders, Osama Ben Laden and Ayman al-Zawahri. Reliable data is scant but various groups may gather hundreds of fighters, including some trained and blooded in the ranks of Hamas but now disillusioned with the ruling movement. For a full study of Salafi groups in Gaza, view this report from the International Peace Research Institute in Oslo here

WHAT MAY BE THE AIM OF THE BOMBINGS?

The attackers hit two heavily guarded Hamas security compounds, one known to include a prison. The second, a residence of President Abbas, is also believed to be used now for detentions and interrogations. If Salafis were behind the bombing, they may be showing both their capabilities and a demand for dozens of imprisoned radicals to be freed.

IS ISRAEL ALSO A TARGET OF RADICALS?

Israel has always been a target for them. The Army of Islam joined Hamas in a border raid in 2006 in which Israeli soldier Gilad Shalit was captured. Shalit is still held and is at the centre of efforts to broker a swap for hundreds of Hamas prisoners. The same group, associated with Gaza's powerful Doghmush clan, has also launched rockets into Israel and fired on troops.

Another group, the Army of the Nation or Jaish al-Ummah, has claimed several rocket attacks against Israel.

Three members of Jund Ansar Allah were killed in an attack in June on an Israeli army position on the border. Some of the attackers rode on horseback.

IS HAMAS AT RISK?

Hamas has thousands of men under arms and easily outnumbers any of these radical groups. Nonetheless, radical ideology and an ability to blend into the population make the Salafis a difficult opponent when they avoid direct confrontation.

Another degree of irritation for Hamas is the Salafis' ability to attack Israel, provoking an Israeli reaction at times when Hamas may be trying to observe a truce.

Hamas officials say they are concentrating on "re-educating" captured radicals, hoping to win them over to a brand of political Islam more in line with Hamas's own principles.