By Asim Tanveer

SARGODHA, Pakistan (Reuters) - U.S. FBI agents and their Pakistani colleagues interrogated on Friday five young American Muslims who wanted to go to Afghanistan to fight U.S.-led forces, Pakistani officials said.

The case is bound to fan fears in Western countries that the sons of immigrants from Muslim countries are being drawn to Islamist militancy, a process made easier by the Internet.

The five men, students in their 20s from northern Virginia, were detained this week in Sargodha in Punjab province, 190 km (120 miles) southeast of the Pakistani capital Islamabad.

The case has again focused attention on nuclear-armed Pakistan's performance in fighting militants as Washington presses Islamabad to root out Islamist fighters crossing the border to attack U.S.-led troops in Afghanistan.

The five men tried to contact militants and stayed in touch with each other through the Internet, Pakistani security officials said, highlighting the difficulty authorities face in trying to track and disrupt plots organized online.

Police in Sargodha took the first step toward filing charges with complaints based on laws pertaining to foreigners and the use of computers to organize crime.

"A case has been registered against the five for violating Pakistan's foreigners and cyber acts," Sargodha police chief Usman Anwar told Reuters.

Pakistani and Federal Bureau of Investigation agents were interrogating the five, said a Pakistani security official.

"They are still in Sargodha and they are being investigated by us as well as the FBI," said the official, who declined to be identified.

Two are of Pakistani origin, one of Egyptian origin, one of Yemeni origin and one of Eritrean origin, officials said.

According to documents issued by the police, the five are named Waqar Hussain Khan, Ahmed Minni, Ramy Zamzam, Aman Yemer and Umar Farooq. Officials said three Pakistani men had also been detained, including two of Farooq's relatives.

The U.S. State Department said a consular officer had determined six of the detainees had U.S. citizenship -- the five young men and one of the others.

"A consular officer visited the detained Americans today in Sargodha," State Department spokesman Ian Kelly said. "The U.S. citizens, each of them signed privacy act waivers but expressly asked that we not speak to the media about their situation."

Kelly said the men were not currently charged with any crime in Pakistan or the United States.

'BRAINWASHED'

The five men would be dealt with according to Pakistani law, Interior Minister Rehman Malik said.