Six international human rights groups have petitioned the United Nations to freeze its counternarcotics aid to Iran until that country abolishes the death penalty for drug offenses.

In a jointly signed Dec. 12 letter released Wednesday by the groups, they argue that the freeze is justified because of “the widening gulf between Iran’s rhetoric and the realities of the justice system.”

Iran executes more prisoners than any other country except China, with 500 to 625 executed last year, according to United Nations estimates. At least half of the condemned were convicted of drug trafficking.

Yury Fedotov, chief executive of the United Nations Office on Drugs and Crime, a Vienna-based agency that has provided millions of dollars to Iran’s counternarcotics efforts, has been in discussions with Iranian officials about the executions, which are at odds with the agency’s human rights guidelines.