The International Committee of the Red Cross is warning that heavy fighting is hampering efforts to rescue civilians and also endangering its staff in the shrinking Sri Lankan war zone.
The International Red Cross says it is imperative more wounded civilians are evacuated from Sri Lanka's north-eastern coast in the days ahead.
The organization is expressing frustration that it took one week to organize a single ferry run to remove 500 Tamil civilians from the war zone and deliver 25 tons of desperately needed food.
ICRC spokesman Marcal Izard in Geneva tells VOA News the latest rescue operation Thursday left some of the injured stranded because of heavy fighting.
"It is too dangerous for the patients, also for ourselves to go there on land and evacuate those people, who are lining up in a row and waiting for this transfer," said Izard. "You need both sides to stop fighting in order for us to go there and take out the people."
The ICRC spokesman describes the situation as "desperate and catastrophic."
"For those who are still there it cannot be worse. I don't know how to describe the situation. I mean those that we can take out they come completely exhausted, dehydrated," he said. "They need really immediately treatment. They are undernourished. It is really extremely difficult because they have been holding out now for weeks or even months."
More food and medicine is needed on shore but there is no guarantee when it will be safe enough to conduct another delivery.
Sri Lanka's military terms its final offensive against the Liberation Tigers of Tamil Eelam, the LTTE, as the "world's largest hostage rescue operation" contending the civilians are being used as human shields by the rebels.
Troops acknowledge facing heavy resistance and sniper fire from the remaining rebel fighters, estimated at no more than 1,000 in number.
The United Nations says as many 100,000 civilians may be trapped in the combat zone.
Sri Lanka's Defense Ministry says troops are no longer using heavy weapons or bombing the area. Reports continue of shelling in the zone. The military says any such explosions are being caused by the LTTE.
Sri Lanka predicts the rebels will be totally defeated on the battlefield any day.
The LTTE once controlled much of the north and east of the island. The army tells VOA the rebels now hold only a two-kilometer long sliver of land between the sea and a lagoon. The Tamil Tigers have been fighting since 1983 to establish an independent ethnic homeland.