Amnesty International has called on Israel to investigate the deliberate contamination of Palestinian farmland - allegedly by Jewish settlers.
Palestinian farmers examine an animal near the West Bank village of Tuwani.
The human rights group said that toxic chemicals had been spread on fields in the Hebron region of the West Bank.
Farm animals had died and farmers had been forced to quarantine their flocks, the organisation said.
It also demanded that Israel put an end to "increasingly frequent" attacks on Palestinians by West Bank settlers.
"These poisoning incidents appear to be part of a deliberate attack on the livelihood of Palestinian farmers in the West Bank," said Kate Allen of Amnesty International UK.
"The Israeli authorities should mount a full investigation and bring the perpetrators to justice."
The chemicals were spread on fields near the villages of Tuwani, Um Faggara and Kharruba in March and April, the group said.
Sheep, gazelle and other animals have been contaminated by the chemicals, and farmers livelihoods had been affected, the organisation said.
According to Amnesty, Israeli and Palestinian scientists who analysed the chemicals spread on the fields found two types of rat poison - one of which is banned in Israel.
Amnesty says that the Israeli authorities have made no attempt to remove the chemicals safely from the fields or to investigate the poisonings.
The villages affected are in a part of the West Bank that is under Israeli military control. Palestinian security services are forbidden by Israel from operating there.
Palestinians also complain of violent intimidation by Jewish settlers in the Hebron area.
In July 2004, Israeli police said they suspected Jewish settlers were responsible for poisoning a Palestinian well in the same area.