The seizure comes ahead of a major international donor conference
Afghan police working with British special forces have uncovered a drugs stash of 237 tonnes of hashish.
Afghan and British officials say they believe it to be the world's biggest seizure of drugs in terms of weight.
The drugs were found hidden in trenches in Kandahar province on Monday. The haul was so large that British jets bombed it to destroy the hashish.
Nato's top general in Afghanistan said the find would seriously cripple the Taleban's ability to buy weapons.
Afghan and British officials said the hashish had a value of more than $400m (£203m).
The Nato-led International Security Assistance Force (Isaf) said the hashish weighed as much as 30 double-decker London buses.
"With this single find, they have seriously crippled the Taleban's ability to purchase weapons that threaten the safety and security of the Afghan people and the region," said Isaf's commander, US General David McKiernan.
Afghan police received a tip about the drugs cache on Monday morning and found it later that day, Isaf said. Three men were arrested during the operation.
The find "reflects the efforts of the Afghan government against the drug trade, and was so large that two aircraft were brought in to destroy the underground bunker in which the hashish was being stored", British Foreign Secretary David Miliband said in a statement.
The BBC's Martin Patience in Kabul says the announcement should provide a welcome boost to the Afghan government on the eve of a major international donor conference in Paris in support of the country.
In the past, Afghanistan has been criticised by the international community for not doing enough to tackle drugs - especially the opium trade.
Afghanistan is estimated to account for 90% of the world's opium.
The previous record drugs haul is believed to be 81 tonnes of cocaine seized in Colombia.