"Syrian forces are committing war crimes by using starvation of civilians as a weapon of war," Amnesty's Middle East director Philip Luther said.
The group said 128 people had died of starvation since regime forces imposed a complete blockade on the Yarmouk refugee camp in July.
"The harrowing accounts of families having to resort to eating cats and dogs, and civilians
attacked by snipers as they forage for food, have become all too familiar details of the horror story that has materialized in Yarmouk," Luther added.
About 51 fell victim to inadequate medical care, Amnesty said, quoting information provided by the Palestinian Red Crescent and human rights groups.
The main hospital in the area, which carried out 600 operations a month before the siege, is now operating without any qualified surgeons or medical supplies, health workers told Amnesty.
Some 17,000 to 20,000 civilians are thought to remain in the camp, Amnesty said.
The United Nations agency for Palestinian refugees, UNRWA, was able to bring in aid in mid-January and again in late February, but had to suspend operations due to clashes.
Last week UNRWA spokesman Chris Gunness tweeted a picture of hundreds of camp residents filling a street lined by ruined buildings as they waited for aid supplies to be handed out.
"Tell me I am not alone at being outraged by this scene in the capital city of a UN member state in the 21st century," Gunness wrote.
In January UN Human Rights Commissioner Navi Pillay warned that the obstruction of aid convoys headed to Yarmouk could constitute a war crime.
According to the UN, 240,000 people are living under siege in Syria, most of them in the Ghouta region around Damascus. Rebels are also besieging government-held villages near Aleppo.
In late February the UN Security Council passed a binding resolution calling for humanitarian access to all areas and an end to the sieges.
In Rome, the UN's World Food Programme (WFP) said that in recent weeks it managed to deliver aid "to areas of Syria that were inaccessible for months," such as rural areas near Homs, Damascus and Dara'a, and camps for displaced people north of Idlib.
WFP deputy director Amir Abdulla warned that aside from providing "temporary relief," the agency "still needs proper and sustained access to people to provide life-saving assistance and also to assess the scale of the needs."
WFP also called for more international donations, saying it needed 309 million dollars to fund its Syrian operations until the end of May. In March, food rations had to be cut by 20 per cent due to budget shortfalls, it reported.
Syria's Palestinian refugees numbered more than 500,000 before the conflict began in March 2011, and according to the UN 63 per cent of them are now displaced.
The community is made up of Palestinians who fled Palestine during the 1948 war that led to the creation of Israel, and their descendants.
UN agencies say that some 2.4 million Syrians have fled the country and 6.5 million are internally displaced, out of a total population of 22.4 million.
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