BBC Middle East analyst Roger Hardy examines claims suggesting an al-Qaeda link to Saturday's twin attacks on synagogues in Istanbul, which killed 23 people and injured more than 300 others. .
Was this al-Qaeda?
Experts tend to agree with the Turkish authorities in suspecting al-Qaeda involvement.
Turkish officials believe there were two suicide attacks using pick-up trucks, and synchronised suicide bombings are an al-Qaeda speciality.
Officials also believe the attack was too sophisticated to have been the work of a local group.
Why would al-Qaeda target Turkey?
The bombings seem to have been a warning to Turkey (a Nato member and an ally of both the US and Israel) that it will suffer severe consequences if it continues to pursue a pro-Western foreign policy.
In addition, Turkey may have been targeted (as Morocco was earlier this year) precisely because it is a predominantly Muslim country where Jews, Christians and Muslims live side by side.
Is this the first time al-Qaeda has targeted synagogues?
Al-Qaeda is thought to have carried out the attack in 2002 at a synagogue on the Tunisian island resort of Djerba.
The attack killed 21 people, mostly foreign tourists.
The al-Qaeda leader, Osama Bin Laden, has repeatedly declared that his global jihad, or holy war, is directed first and foremost at "Crusaders and Jews".
In practice, however, most of the group's operations have been directed at America and its allies in the Muslim world.
What sort of reaction has it prompted in Turkey?
There is shock and outrage in Turkey, coupled with a good deal of solidarity with the country's small but long-established Jewish community.
Turks have not failed to notice that while Jews may have been the main targets, most of the dead were Turkish Muslims who had found themselves in the vicinity of the two synagogues.
What more can be done to prevent such attacks?
The Turkish authorities have pledged to increase security around possible targets in Istanbul - not easy in a big, bustling city which attracts tourists from all over the world.
If the attack over the weekend was indeed the work of al-Qaeda, the group has once again shown it is capable of springing surprises.
This year the network, or groups affiliated to it, has struck Casablanca in Morocco, the Saudi capital Riyadh (twice) - and now, apparently, Istanbul.