United Nations aid agencies working in the conflict-hit areas have said that 112,000 people had been internally displaced in the past two months and warned that "the figure is expected to increase."
Amnesty said restrictions on travelling to rebel-held areas had blocked supplies getting in.
"These people are running out of places to go and basic necessities," said Yolanda Foster, Amnesty International’s Sri Lanka researcher.
"The Tigers are keeping them in harm’s way and the government is not doing enough to ensure they receive essential assistance."
Amnesty accused the the Liberation Tigers of Tamil Eelam (LTTE) of imposing a pass system and in some cases forcing family members to stay behind to ensure the rest of the family return to areas under rebel control.
"These measur