COLOMBO (AFP) - Sri Lankan troops have seized a Tamil Tiger command centre in the island's north as ground troops advance further into the rebels' remaining territory amid heavy fighting, the military said on Thursday. Security forces found briefing rooms containing detailed maps at the facility in Mullaittivu district, where the Liberation Tigers of Tamil Eelam (LTTE) have been penned in after a series of battlefield defeats. "We have captured the main LTTE command centre in Dharmapuram," army spokesman Brigadier Udaya Nanayakkara said, adding that troops were conducting clearance operations in the area. He said soldiers also found a communications room within the complex, but that the guerrillas had dismantled the equipment and removed it as troops moved in Wednesday. "We think it is a very significant place because they had maps of our brigade-level camps," Nanayakkara said. "This must have been a key centre they used." However, they have steadily lost ground for 18 months ago and have now been confined to the jungle and lagoon district of Mullaittivu where they are known to have several military bases. Sri Lanka's army has said it hopes to crush remaining rebel resistance by April after weeks of fighting that have been among the most violent of the bitter ethnic conflict. As the rebels retreated, the whereabouts of their leader, Velupillai Prabhakaran, 54, remains unknown, with latest reports suggesting he may have fled the island and possibly headed to south east Asia. Malaysian police chief Musa Hassan told the New Straits Times in Kuala Lumpur that his men were "using our local intelligence network to ascertain if he is already in the country." Sri Lankan army chief Sarath Fonseka said recently that Prabhakaran may have already escaped by sea as his forces were surrounded. The LTTE are banned across Europe Union member states, Australia and the United States. There is an international arrest warrant against Prabhakaran for his involvement in the 1996 bombing of the Central Bank of Sri Lanka building, which killed 91. The United Nations on Thursday accused the Tigers of blocking some of their staff and their immediate families from leaving the Mullaittivu area in a convoy that brought food and emergency supplies to displaced people. "The UN calls on the LTTE to meet their responsibilities and immediately permit all UN staff and dependants to freely move from this area," the UN said in a statement. It also raised new concerns for the safety of civilians trapped inside territory still held by the Tigers. The Tigers have not commented on their recent setbacks but the pro-rebel Tamilnet.com website Thursday accused the military of shelling a makeshift hospital in Mullaittivu. It said 46 civilians were killed and 176 wounded within a 60-hour period. "There are several dead bodies on the sides of the road and under the trees of the hospital," the report said, adding that medical staff and patients sought refuge in nearby bunkers to avoid continuous shelling. Local officials in the northern government-held town of Vavuniya said that 60 civilians who were caught in the cross-fire had been brought to the main hospital in the region on Thursday. It was not immediately clear who was responsible.