Tariq Mahmud, 30, who has dual British and Pakistani nationality, has been "detained by our authorities," spokesman Masud Khan told reporters, scotching rumours that he was being held by US forces in neighbouring Afghanistan.
"He is being investigated on suspicion of having links with al-Qaida... I cannot tell you his whereabouts and how the investigations are being carried out."
Mahmud, from Birmingham in central England, was arrested in late October from a house in the garrison city of Rawalpindi, near Islamabad.
The British Foreign Office was aware of the arrest and is seeking further information from Pakistani authorities, a spokesman told Aljazeera.net earlier on Monday.
''We are pressing the Pakistanis to allow our consulate to make contact with this individual. We have sent the Pakistanis a photocopy of Mr Mahmud's passport and some photographs to assist them with their inquiries,'' said the spokesperson.
Pakistan, a former ally of Afghanistan's ousted Taliban rulers whose loyalty switched to the United States following the 11 September 2001 attacks, has arrested more than 500 al-Qaida suspects on its soil, including three key bin Ladin associates.
The majority of those arrested are now in US custody at the US Guantanamo Bay detention centre in Cuba. Nine Britons are among about 660 detainees being held without charges or access to lawyers.