ISLAMABAD (AFP) - A steady, modest flow of Western militants plotting to launch bomb attacks abroad continue to trickle into Pakistans lawless northwest for training, Pakistani and Western officials say. As Pakistani authorities detain two Frenchmen picked up in Lahore on suspicion of links with the mastermind of the 2002 Bali bombings, diplomats say many more suspects are holed up in Taliban and Al-Qaeda enclaves. A host of bombings and aborted attacks in Western cities in recent years linked to the tribal area form evidence of the real threat posed by this small but hard-to-detect band of migrating militants. Bombings in Madrid in 2004 and London in 2005, a foiled plot in Barcelona and the Mumbai siege in 2008, as well as the botched plot in New Yorks Times Square in May last year, all led back to Pakistans tribal areas. Al-Qaeda receives logistical support from the Pakistani Taliban who have trained up hundreds of suicide bombers responsible for the majority of the 4,200 people killed in attacks across Pakistan in the past four years. Diplomats say the most difficult foreigners to track down are British and Americans of Pakistani origin, as they arrive with legitimate visas and blend in with the local population as they make their way to the Waziristan region. The British-born Pakistanis are mostly young boys who are adventurous by nature and dont find it hard to come to Pakistan and move around, a security official told AFP last year, requesting anonymity. There are some basic flaws in our immigration system. Its very easy for these suspects to pass through, another senior security official said. The French who come are mostly of North African origin and number twenty or thirty in rebel camps along the Afghan-Pakistan border, according to sources familiar with the matter. Ten or fifteen at most have been identified, according to an official who requested anonymity. Two French youths arrested about ten weeks ago in Lahore are suspected of being part of an Al-Qaeda-linked group responsible for the 2002 Bali nightclub attacks that killed 202 people, officials told AFP. They were arrested by police hunting Indonesian militant Umar Patek, a suspected mastermind of the Bali attacks, blamed for a string of deadly bombings across Indonesia. Five German militants were killed in October last year by a US drone strike on a militant hideout in the tribal district bordering Afghanistan. Most of the militants arrive with a working knowledge of the local language, Pashto, and wear local dress, making them difficult to identify, an intelligence official said. Retired Brigadier and security analyst Mehmood Shah, a former security chief in the tribal areas, said local facilitators and handlers meet the European fighters on arrival in Pakistan and later send them on to the tribal region. Al-Qaeda converts these people to their cause before they arrive... once foreigners arrive in North Waziristan they are already fully motivated, he said.