The five, described as students, were taken to court after being arrested two days earlier in west and southwest Turkey.

One is believed to have been designing computer programs to jam the flight controls of drone aircraft and the others were involved in fund-raising for militants, the official said.

The arrests come hard on the heels of a security scare last month in Europe. Intelligence sources said at the time that a German interrogated by US troops in Afghanistan had revealed details of a plot to attack European targets.

The number of Turks fighting in the Afghanistan-Pakistan region is believed to be relatively small, though a senior security official in northwest Pakistan told Reuters there had been an increase over the past year.

“We detained five men from five different cities — Hatay, Istanbul, Kayseri, Antalya and Izmir,” said the official, who requested anonymity because of the sensitivity of the information. “These people belong to an Aegean branch of Al-Qaeda. The leader is currently in Afghanistan, fighting for Al-Qaeda.”

The leader of the group was named “Zekeriya” and served time in prison before joining the insurgency against Afghan and US-led forces in Afghanistan, said the official.

A NATO member, with troops serving in non-combat roles in Afghanistan, Turkey has been a venue for Al-Qaeda attacks in the past.

Graduates of Bin Laden’s training camps were behind the bomb attacks in 2003 that killed 57 people and wounded hundreds in Istanbul, alerting the government to the need to monitor any rise in the number of Turks going to Pakistan and Afghanistan.

The Turkish official said the suspect that had been arrested in Izmir was a 23-year-old mathematics student named Abdulkadir Kucuk who was designing programs to jam unmanned drones.

He was also a bombmaker, the official said, and is believed to have been in e-mail contact with Zekeriya. The JihadiMedia website says a man with the name Zekeriya Cifti served a one-year jail sentence in Turkey.

The others arrested in Turkey this week were involved in fund raising for the militants, the security official said.

“We have bills, images, everything to prove they’ve been sending money to Afghanistan. Clear evidence,” he told Reuters.

Turkish police often arrest suspected militants and describe them as having links to Al-Qaeda, though details seldom emerge. Around 120 Al-Qaeda suspects were rounded up last January in raids mostly carried out in the southeast.

Turks have until now played little part in Al-Qaeda’s global jihad, but security analysts have noted an increase in the number of Turkish language jihadi websites, some of which have posted obituaries for Turkish militants killed in Afghanistan.

Some of those websites promote the Islamic Movement of Uzbekistan (IMU), a Central Asian jihadi movement with ties to Al-Qaeda.

The security official said Zekeriya was a commander in a group led by a fellow Turk called Ebuzer, the nom de guerre of Serdar Erbashi, according to the Washington-based Jamestown Foundation.

A veteran of the Chechnya conflict, Ebuzer is said to be the leader of Taifatul Mansoura, the Victorious Assembly, a militant band that sprang from the IMU and has been based in Afghanistan and the Pakistani tribal agency of North Waziristan.