The rebels have been accused of seriously violating international law
Tamil rebels in Sri Lanka are breaking international law by using civilians as buffers against the army, human rights group Amnesty International says.
A researcher for the organisation said there were cases where militants had forced people to stay in rebel-held areas to hamper army operations.
She said the government was not doing enough to help them.
There has been no word from the rebels or the government in relation to the latest Amnesty claims.
Amnesty has accused both sides in Sri Lanka's long-running conflict of deliberately putting civilians at risk
Tamil people in the conflict zone "are running out of places to go and basic necessities", Amnesty International's Sri Lanka researcher, Yolanda Foster, told the AFP news agency.
"The Tamil Tigers are keeping them in harm's way and the government is not doing enough to ensure they receive essential assistance."
Amnesty accused the Tamil Tigers of imposing a pass system - and in some cases forcing family members to stay behind - so that other family members would come back to areas under rebel control.
"These measures seem designed in part to use civilians as a buffer against government forces - a serious violation of international humanitarian law. The Tamil Tigers have also engaged in forced recruitment," the Amnesty report said.
Government bombardments and shelling since May have forced thousands to flee their homes, primarily in Kilinochchi and Mullaittivu districts, the London-based rights group said.
On Thursday, the International Committee of the Red Cross said tens of thousands of people had been displaced in recent fighting in northern Sri Lanka.