The government says more and more civilians are fleeing rebel-held areas
The International Committee of the Red Cross (ICRC) says it has evacuated a further 160 sick and wounded people trapped by fighting in north Sri Lanka.
An ICRC spokeswoman told the BBC that a vessel was on its way to Trincomalee after collecting civilian patients from the coastal village of Putumattalan.
Meanwhile the British PM has appointed a former Defence Secretary, Des Browne, as his special envoy to Sri Lanka.
The Red Cross says recent fighting has claimed hundreds of civilian lives.
It says that tens of thousands of people are trapped.
"Some of those we have collected are in a serious medical condition and need urgent treatment," the ICRC spokeswoman said.
She said the vessel would arrive in Trincomalee late on Thursday.
The spokeswoman said that the ICRC had no knowledge at present of further injured or sick civilians who needed to be evacuated.
British Prime Minister Gordon Brown said that Des Browne would work closely with the Sri Lankan government and leaders from all communities.
The British PM wants an end to the fighting
He said the need to get a ceasefire and find a political settlement had to be addressed immediately.
"I want him to be involved in seeing whether there is scope for political progress in Sri Lanka as well as looking at the issues of humanitarian aid," the British prime minister said.
"The important thing is to emphasise to all partners that without a ceasefire and then an attempt at a political process we will be back to the same problems that we've had before."
In a separate development, the army says it has disbanded a "safe zone" it had established in the war-hit north.
Military spokesman Brig Udaya Nanayakkara said that the army was instead setting up what he called a new refuge for tens of thousands of civilians trapped in the area.
He accused Tamil Tiger rebels of forcing civilians to seek shelter from the fighting out of the original zone, forcing the government to set up a new one.
There has been no word from the Tamil Tigers in relation to the government's announcement, but the pro-rebel TamilNet website has repeatedly accused the army of shelling within the zone.
The government established the first zone on 21 January in a small area of land inside rebel-held territory. Security forces encouraged families trapped in the war-affected areas to move to the refuge and pledged not to attack that area.
About 50,000 soldiers are pressing the Tamil Tigers into a patch of north-eastern jungle after taking the key areas of Kilinochchi, Elephant Pass and Mullaitivu.
The government has rejected international calls for a ceasefire, demanding the rebels lay down their arms.
The Tigers have said they will not do so until they have a "guarantee of living with freedom and dignity and sovereignty". The rebels started fighting in the 1970s for a separate state for Tamils.