Three groups working to get countries to abolish the death penalty have appealed to the United Nations to freeze anti-drug assistance to Vietnam after the communist country sentenced 30 people to die for drug-related offenses.

The call from Harm Reduction International, Reprieve and the World Coalition Against the Death Penalty cites the United Nations Office on Drugs and Crime's internal human rights guidance requiring the organization to stop funding for a country if it's feared that such support may facilitate executions.

"Our organizations have, for many years, been raising concerns about UN assistance for drug enforcement in countries that continue to apply the death penalty for drug offences," said the letter, which was sent to the UN resident coordinator in Vietnam and the UNODC country manager.

The appeal comes after a court in northern Vietnam sentenced 30 people to death last month for heroin trafficking, the largest number of defendants sentenced to death in a single trial in the country's court history.

UNODC officials were not immediately available for comment Wednesday.

UNODC aid to Vietnam will exceed $5 million for technical assistance, equipment, training and other support for the 2012-2017 period, the letter said. Drug control is the largest component of the program.

There are nearly 700 people on the death row in Vietnam.