The Centre has extended the ban by two years on Liberation Tigers of Tamil Eelam (LTTE), declaring it as an unlawful association.The notification to this effect was issued on Wednesday, a Home Ministry release said on Thursday.The LTTE, also known as Tamil Tigers, is a militant group that has waged a violent campaign against the Sri Lankan government since the 1970s in order to create a separate Tamil state in the northern and eastern part of the island nation.The group-led by V Prabhakaran has been proscribed as a terrorist organisation by several countries including the United States.The LTTE was involved in the assassination of former Indian prime minister Rajiv Gandhi in May 1991.