A Vietnamese court has sentenced four men to death for drug dealing, adding to prisoners in limbo on death row amid a shortfall in lethal injections used for such executions.

The four were convicted on Wednesday for dealing 50kg of heroin in northern Vietnam, the state-run Laborer newspaper said.

Trafficking or trading 600 grams (1.3 pounds) of heroin is punishable by death in Vietnam, a country with some of the world’s toughest drug laws.

While their fates are sealed with the verdict, they will have to fall in line with hundreds of others still awaiting their punishment.

Vietnam has changed its death sentence from firing squads to lethal injections on humanitarian grounds.

But a EU ban on the exports of drugs used in lethal injections have hampered executions, causing prisoners to languish in their cells.

There are currently more than 500 people on death row in Vietnam, reports The Associated Press.