Turkish officials are investigating claims that the al-Qaeda network carried out Saturday's attacks against synagogues in Istanbul.
Prime Minister Erdogan says justice will be done
On Sunday the London-based Arabic newspaper al-Quds said it had received a statement from al-Qaeda in an email.
It said the group targeted the synagogues because Israeli agents were working there, Al-Quds Editor Abdel-Bari Atwan told the BBC.
At least 23 people were killed and more than 300 wounded in the bombings.
Prime Minister Recep Tayyip Erdogan is due to call a cabinet meeting on Monday to discuss the attacks.
"Our security teams, our intelligence services have to work to determine the extent of truth of the claims," he said.
Hard to check
On Sunday Mr Atwan told the Arabic satellite TV channel al-Jazeera that the statement was from an al-Qaeda division called Brigades of the Martyr Abu Hafz al-Masri.
That division had claimed responsibility for the attack on the United Nations headquarters in Baghdad - which killed 23 people in August.
Analysts say it may be impossible independently to confirm that the latest statement comes from al-Qaeda.
An earlier claim to the attacks was made by a Turkish group called the Islamic
Front of Raiders of the Great Orient.
But the BBC's Richard Galpin in Istanbul says Turkey was quick to point the finger at international radical groups.
The level of sophistication required to carry out the attacks was beyond any local organisation, our correspondent says.
The bombs, which went off minutes apart outside synagogues in the districts of Beyoglu and Sisli, badly damaged both buildings and scattered wreckage over a wide area.
According to Turkish media reports, the attacks were caused by suicide bombers driving two trucks, each loaded with 400 kilograms of explosives.
Israeli Foreign Minister Silvan Shalom visited the bombed synagogues, accompanied by the mayor of Istanbul and the city's chief rabbi.
He laid wreaths at the sites as Turks threw down white carnations in a sign of condolence.
Our correspondent says his visit was clearly intended to signal that Israel and Turkey would co-operate closely in the aftermath of the bombings.
Most of those killed in the attacks were Muslim Turks, who lived, worked or were passing by the synagogues when the explosions occurred.
Six Jews were also among the dead.