Bangladesh has tightened security at its international airports after intelligence sources warned of possible hijackings or terrorist attacks, airport officials said Friday. Special security measures had been taken at Dhaka's Shahjalal International Airport on Thursday night, followed by similar moves at the Sylhet and Chittagong airports, the officials said. They and police would not say if they received any specific threat. “We ... called in extra police and deployed security squads especially formed to tackle terror activity,” said one Dhaka security official, who asked not to be identified. Media quoting unnamed intelligence sources reported over the past few days that the airports could be targets of terror attacks. Bangladesh had been concerned about attacks since a series of bombings in 2005 by outlawed groups killed dozens of people. In recent months Bangladesh police have arrested several Lashkar-e-Taiba activists and militants from other groups who have been hiding and training in Bangladesh. They told police during interrogation that they drew funds from outside Bangladesh through various financing agencies and non-government organizations. Home Ministry officials said they were aware of threats by militants. They say the militants kept a low profile after six top leaders of two outlawed groups – the Jamaat-ul-Mujahideen and the Jagrata Muslim Janata – were hanged in early 2007, but have lately been showing signs of more activity. Concerns have grown as Bangladesh prepares to hold war crime trials, with key leaders of the Jamaat-e-Islami party likely to be among the accused. Jamaat, an ally of the main opposition Bangladesh Nationalist Party, is accused by critics of helping the Pakistani Army in what Dhaka says were acts of genocide during Bangladesh's 1971 war of independence. Jamaat denies the charge and says the proposed trials are a political vendetta by Prime MInister Sheikh Hasina's Awami League.