COLOMBO (AFP) - Sri Lankas Tamil Tiger rebels accused government forces of killing at least 49 people Tuesday in an artillery and mortar attack on a hospital, a charge fiercely denied by the islands military. The accusation came amid mounting international outrage over large-scale civilian deaths, with the European Union calling for UN Security Council action and the US telling Sri Lanka to stop using heavy weapons. A spokesman for the Liberation Tigers of Tamil Eelam (LTTE), whose fighters are battling to defend a tiny strip of coastal jungle, said a makeshift hospital packed with survivors of weekend attacks was hit by government forces. Heavy artillery and mortar attacks this morning hit the hospital and 49 people were killed there, rebel spokesman S Puleedevan said by telephone. Most of them were those injured in Sundays attacks. The pro-rebel Tamilnet website said the number of killed had since risen to 49, and that 55 patients were wounded. The LTTE says more than 2,000 civilians were killed in similar alleged Sri Lankan army attacks on Sunday. Sri Lankas Defence Ministry however blamed any civilian deaths on the rebels - who it accused of firing heavy weapons from inside an area declared to be a civilian safety zone. The military insists it is not using heavy guns, and says the Tigers are keeping people hostage to use them as human shields and shooting those who try to escape.We are not using heavy artillery or any heavy weapons. If not for the civilians, it would take about 72 hours to defeat the LTTE, military spokesman Brigadier Udaya Nanayakkara told reporters. The rival claims cannot be independently verified as independent journalists, diplomats and most aid agencies are barred from going anywhere near the conflict zone in the far northeast of the island. The Defence Ministry said its troops had captured more ground in the latest fighting and had recovered 35 rebel bodies. The military spokesman said the LTTEs leader, 54-year-old Velupillai Prabhakaran, was now trapped. According to our information, the LTTE leadership, along with their second-rung, is remaining in the small area, Nanayakkara said. Meanwhile, the International Committee of the Red Cross on Tuesday demanded unimpeded access to Sri Lankas war zone to save the lives of hundreds of wounded civilians.The ICRC said it could not operate a mercy mission to ferry out the wounded from the small sliver of coastal land still in the hands of the Tamil Tigers on Tuesday because of continuing fighting. The plight of the people remaining in the combat area is desperate, said Paul Castella, the head of the ICRC delegation in Sri Lanka. We need unimpeded access to them in order to save lives. As the fighting draws ever closer, thousands of people trapped along a narrow coastal strip north of Mullaittivu are forced to take cover most of the time in improvised trenches and shelters in order not to be hit by exchanges of fire between government troops and fighters of the Liberation Tigers of Tamil Eelam (LTTE), the ICRC said in a statement. It said the civilians also suffered from a lack of food, drinking water and proper medical care.