The suspect, identified as Syrian national known as "Luia Sakra," is believed to be the top figure in Osama bin Laden's al-Qaeda network in Turkey, was apprehended in the southeastern city of Diyarbakir on Sunday as he attempted to board a plane for Istanbul, the sources said.

Second suspect also detained

Also Wednesday, judges ordered the arrest of another Syrian national on charges he is Sakra's courier, the sources said.

They said the suspects were detained in Turkey's largest city of Istanbul and in the Mediterranean tourism hub of Antalya.

The reports followed remarks by Israel's counter-terrorism chief who on Tuesday said Turkey had caught al-Qaeda-linked terrorists who were planning attacks against foreign tourists.

Israel this week diverted four cruise ships from Turkey to Cyprus and urged its citizens to avoid Turkey's popular southern coast, citing "concrete and grave terror threats" against them.

PLASTIC SURGERY

Security sources said Sakra, considered an expert bomb maker, had undergone plastic surgery and was attempting to fly to Istanbul under an assumed name for a second operation. He arrived in Diyarbakir from Antalya.

Sakra is thought to be responsible for al-Qaeda's cells in Turkey and to have played a key role in bombings in Istanbul in November 2003 that killed more than 60 people.

A Turkish al-Qaeda cell claimed responsibility for those attacks, which struck two synagogues, the British consulate and London-based HSBC bank in one of Turkey's worst episodes of peacetime violence.