Istanbul, Turkey ? Authorities arrested six people in connection with the suicide bombings of two Istanbul synagogues as opposition leaders accused Turkey’s government on Wednesday of being too lenient toward Muslim radicals.

The suspects include relatives of two accomplice suspects in the bombings, the Anatolia news agency said. A Turkish court charged five with “attempting to overthrow the constitutional structure,” which carries a sentence of life imprisonment. A sixth person was charged with “helping illegal organizations,” punishable by five years in prison, Anatolia said.

No trial date has been set.

Two suicide attackers, both Turks, blew up pickup trucks outside the synagogues on Saturday, killing 23 people and the two bombers. Foreign Minister Abdullah Gul said the two had visited Afghanistan in the past and that investigators were looking for any al-Qaida links.

Istanbul Gov. Muammer Guler identified the bombers as Mesut Cabuk, 29, and Gokhan Elaltuntas, 22, both from the southeastern town of Bingol.

The role of local militants could mean trouble for the government of Prime Minister Recep Tayyip Erdogan, which has its roots in an pro-Islamic party. Opposition leaders criticized his government for backing off a countrywide crackdown on militant Islamic groups after coming to power a year ago, and even releasing hundreds of Islamic militants from prison under a four-month-old amnesty.

Al-Qaida claimed responsibility for the bombings Sunday, but it was not possible to authenticate those claims.

An outlawed Turkish radical group called the Islamic Great Eastern Raiders’ Front, or IBDA-C, also claimed responsibility, but Turkish authorities said the attack was too sophisticated to be carried out by that group.