Five men have been detained in the Afghan capital, Kabul, with 10,000 kilogrammes of material which could be used in bombs, intelligence officials say.
The men intended to use the material in multiple attacks in crowded areas, according to the officials.
"If 10,000kg of explosives in a city of seven million people had been detonated in, what would have happened?" Shafiqullah Tahiri, a spokesman for the National Directorate of Security, said on Saturday.
He said three of the men detained were Pakistani citizens, while two were Afghans. All five have confessed to their involvement.
The material had been found on a lorry registered in Pakistan, under potato sacks.
One of the arrested Afghans was allegedly a Taliban commander and two of the Pakistanis had links to the Pakistani intelligence agency, the spokesman said.
Al Jazeera's Bernard Smith, reporting from Kabul, said the confiscated bags contained ammonium nitrate.
"This is a key component used for making bombs in Afghanistan, particularly for home-made roadside bombs," he said.
"Only last month, [a commander] of the NATO forces here complained to the US senate that he wasn't getting as much co-operation as he deserves from the Pakistanis in stopping ammonium nitrate crossing the border.
"It's not the first time that this kind of material has been seized coming into Afghanistan. It's a big concern."
The Afghan officials said the accused had confessed to loading the explosives onto the lorry in the Pakistani city of Peshawar, and that the materials were to be used in roadside bombs and suicide vests.
The officials also gave further details of an alleged assassination plot against Karim Khalili, Afghan vice-president, which was foiled on Sunday.
Three suspected attackers had been detained with detailed map of Khalili's house and nearby security checkposts, the officials said.
The announcement of the arrests comes just days after Kabul was rocked by the largest Taliban attack of the past decade, with armed men holding three important areas in the city under siege for several hours.
The sole surviving Taliban fighter from Sunday's co-ordinated attacks reportedly confessed to being member of a 200-strong suicide squad trained in Pakistan, raising fears of similar attacks in the future.
Ryan Crocker, US ambassador to Afghanistan, said there was "no question" that the Haqqani network, which the US believes is based in Pakistan's North Waziristan region, mounted the assault.
Crocker called on Pakistan to crack down on the Haqqanis and said the response to that demand would influence future ties between the strategic allies.
Abullah Shahood reported from Kabul.