Turkish and Israeli investigators are probing the terror bombing of two synagogues in Istanbul as the death toll from the massacres rose to 23 with the discovery of three more bodies.

Israeli Foreign Minister Silvan Shalom flew to Istanbul to show solidarity to the small Jewish community in this predominantly Muslim nation that is an ally of Israel.

Flanked by Istanbul's chief rabbi, Isak Haleva, who was among the more than 300 wounded in Saturday's twin attacks, Shalom laid a wreath in the rubble outside one of the two synagogues. Turks, kept behind security barriers by police, threw down white carnations in a sign of condolence.

Private NTV Turkish television said intelligence officials reportedly were questioning three people, including two women, about the bombings, which authorities suspected could be the work of international terrorists, possibly al-Qaida.

The head of Istanbul's health department, Erman Tuncer, said three more bodies were found, raising the death toll to 23 from 20.

Striking minutes apart on Saturday in two neighbourhoods three miles apart in this metropolis as Jews worshipped on their Sabbath morning, the bombings claimed most of their victims among Muslims who were passing by.

Together, investigating teams from both nations probed the twisted metal and other rubble for possible links to Osama bin Laden's organisation or other terrorist groups based abroad.

One of the blasts tore apart the facade of Neve Shalom -- Istanbul's biggest synagogue and the symbolic centre of Turkey's 25,000-member Jewish community.

The other synagogue was Beth Israel, in an affluent neighbourhood.

Authorities were sceptical about a Turkish radical Islamic group's claim that it carried out the bombings, questioning whether it was capable of carrying out such carefully co-ordinated attacks. Turkish officials said intelligence suggested al-Qaida may have been planning attacks in Turkey.