Bangladesh imposed a travel ban on Monday on 40 people, mostly leaders of the opposition Jamaat-e-Islami party, over alleged war crimes during the country's war of independence four decades ago. The party has denied charges that it collaborated with the Pakistani army during the 1971 war, and has accused the government of Prime Minister Sheikh Hasina of concocting war crimes charges to try to undermine it.Jamaat is the main ally of the opposition Bangladesh Nationalist Party of former prime minister Begum Khaleda Zia. Those banned from leaving the country included Jamaat chief Motiur Rahman Nizami, his deputy Ali Ahsan Mohammad Mujahid, and another key leader, Delwar Hossain Saidee - who were arrested last month on charges ranging from obstructing police to sedition. Immigration officials at Dhaka' said they had received instructions from the government not to allow them to leave the country.