Amnesty International on Friday urged world leaders at a Geneva conference on the Syrian conflict not to sacrifice human rights for the sake of a political settlement.
It called on Saturday's meeting "not to pursue any policy of issuing amnesty or any other similar measure for crimes under international law as part of any peace plan."
"Stopping the killing must be everyone's priority, but it would be immensely damaging should the international community be tempted to offer those responsible for crimes against humanity or war crimes a get-out-of-jail-free card," Amnesty said in a statement.
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"It is UN policy that there should be no amnesty for crimes under international law," the rights group said.
"But we have already seen how this policy was ignored in Yemen, where an immunity law has been enacted, in the interest of a negotiated settlement," said Ann Harrison, the organisation's Middle East and North Africa deputy director.
Saturday's conference is due to be attended by US Secretary of State Hillary Clinton and the foreign ministers of Russia, Britain, China, France, Iraq, Qatar, Turkey and Kuwait.
Amnesty urged the meeting of world powers to push for human rights monitoring in Syria, where monitors say more than 15,800 people have been killed in the suppression of an anti-regime revolt since March 2011.
"We are looking to the participants to give attention to the need for a human rights monitoring presence in Syria which could monitor, investigate and publicly report on crimes against humanity, war crimes and human rights abuses by all sides," said Harrison.