The Turkish government says a number of people have been arrested over a double bombing last week in Istanbul that killed 17 people.
The bomb blasts, which occurred about 10 minutes apart on a busy street, were the worst such attacks Turkey since 2003, when al Qaeda carried out a series of bombings in Istanbul.
Some 150 people were also injured in last Sunday's blasts.
Interior minister Besir Atalay blamed Kurdish separatist rebels for the explosions and said most of those involved had been detained.
Although he did not specify how many people had been arrested, a prosecutor said separately that eight suspects should be charged with membership of the Kurdistan Workers Party, or PKK.
"Our judgement is that this merciless attack was the work of the bloody separatist group," Interior minister Besir Atalay told a televised news conference.
"Those who helped, those who gave shelter and those who took part in the attack have been caught."
The Kurdistan Workers' Party has denied any role in the attacks. It is considered a terrorist organisation by the US and EU, as well as Turkey.
PKK leader Zubeyir Aydar said his group was not linked to the attacks, suggesting they might have been carried out by "dark forces", in an apparent reference to ultra-nationalists.
Some 40,000 people have been killed since the PKK launched its campaign for self-rule in mainly Kurdish south-east Turkey in 1984.