Washington's top international narcotics official gave a qualified go-ahead for countries to decriminalize drugs on Tuesday — the latest sign that the US is walking back decades of hardline rhetoric ahead of a pivotal special session of the United Nations General Assembly on global drug policy in April.

Speaking to reporters at the US Mission to the United Nations in New York, William Brownfield, assistant secretary of state for international narcotics and law enforcement affairs, said American officials were attempting to "find areas of pragmatic reform" with other member states over drug policy. A consensus outcome document currently under negotiation at the Committee on Narcotic Drugs in Vienna is expected to be finalized by the middle of next week, he said, and will be presented at the UN special session (UNGASS).

In recent years, Brownfield has increasingly articulated a policy of flexibility in interpreting the three UN drug conventions that have guided domestic laws since the first was agreed upon in 1961. On...