( CNN ) -- Artillery shells slammed into a hospital Sunday in the northern Sri Lankan district of Mullaittivu , where civilians -- including a growing number of children -- are being treated as government forces and Tamil rebels continue to clash . A Sri Lankan soldier walks through Mullaittivu , the former military headquarters of the Tamil rebels . More than 200 civilians and at least 30 children have been injured in the last three days of fighting , a relief worker told CNN Sunday . `` That is the absolute minimum ( number of injured ) , '' the aid worker , who did not want to be identified for fear of jeopardizing the work of relief organizations , said . Government officials are accusing aid organizations and foreign media of sensationalizing civilian casualties . `` It looks as if it 's convenient for certain agencies to exaggerate the numbers so that this can be converted to a humanitarian crisis in the public eye , `` Secretary of Foreign Affairs Dr. Palitha Kohona told CNN . On Sunday , Sri Lankan Defense Secretary Gotabaya Rajapaksa promised to `` continue with the military offensive until we liberate the remaining area under LTTE ( the rebel group ) control , '' according to Sri Lanka 's state-run news agency . Watch a report on civilians caught in fighting » . A `` handful '' of United Nations staff are working around the clock to save a growing number of children caught in the crossfire , a U.N. spokesman said Saturday . Children as young as 4 months old were being treated in local hospitals for shrapnel injuries and other `` wounds of war , '' spokesman James Elder told CNN . `` There is just intense fighting in a small area where children and other civilians are , '' Elder said . `` The space ( where conflict is taking place ) is shrinking and the fighting is augmenting . '' Thursday , U.N. aid workers rescued 50 critically injured children and 105 adults , he said . `` We are trying to get as many people out of there as we can , '' Elder said . Humanitarian groups say as many as 250,000 unprotected civilians are trapped in the area . Sri Lankan President Mahinda Rajapaksa has promised to allow safe passage to trapped civilians and urged the Tamil Tigers to promise the same . `` We have declared a safe zone for civilians , the coordinates of which were announced by the security forces , '' Rajapaksa said on his government 's Web site . `` It is unfortunate that the ( Tamil Tiger group ) is exploiting this declared safe zone for civilians by placing their heavy artillery within the safe zone and using it as a launching pad to attack security forces and indiscriminately kill civilians . '' The fighting has created a `` nightmarish '' situation for civilians in the conflict zone , Elder said . An emerging shortage of humanitarian supplies and diminished access to clean water , sanitation , and food are compounding a crisis , he said . Sunday , Sri Lankan soldiers seized a key rebel stronghold in a surprise attack deep in Tamil held territory . Troops crossed a lagoon and entered the town of Mullaittivu before encountering heavy resistance from Tamil fighters , according to the government-run news agency . The The Liberation Tigers of Tamil Eelam ( LTTE ) -- commonly known as the Tamil Tigers -- have fought for an independent homeland for the country 's ethnic Tamil minority since 1983 . The civil war has left more than 70,000 people dead .
Sri Lankan hospital hit by artillery shells . Children young as 4 months treated in local hospitals for shrapnel injuries . Aid workers rescue 50 critically injured children and 105 adults . Sri Lankan President has promised to allow safe passage to trapped civilians .