The UN Security Council has voiced grave concern for the first time over civilian deaths in the war in Sri Lanka.
It ordered the army and the Tamil Tiger rebels to protect civilians.
The resolution was passed unanimously on Wednesday. It reads: "The members of the Security Council express grave concern over the worsening humanitarian crisis in northeast Sri Lanka, in particular the reports of hundreds of civilian casualties in recent days."
A Red Cross worker was killed inside the war zone on Wednesday.
Hundreds of civilians were reported killed on Sunday and Monday by artillery fire when troops attacked a narrow strip of land held by the Liberation Tigers of Tamil Eelam.
Russia, China, Vietnam and Libya oppose any formal council action on what they see as an internal Sri Lankan matter.
The statement said the council members "strongly condemn the LTTE for its acts of terrorism over many years" and urged the group to "lay down its arms and allow the tens of the thousands of civilians to leave."
UN officials say the rebels are using civilians as human shields.
The Security Council also voiced "deep concern" about reports of continued heavy shelling by government forces in the conflict zone - reports that the Sri Lankan government has repeatedly denied.