Afghan police seized four tonnes of sodium nitrate, used in the making of car bombs and improvised explosive devices, officials said, in one of the largest such seizures in the country's 19-year insurgency.
The chemical was seized from a truck in Kabul on Sunday. The driver had been arrested and investigations were under way, interior ministry spokesman Tariq Arian said.
The government has not said which militant group was responsible. Sodium nitrate is also used in fertilisers and preservatives but it has been banned in Afghanistan for years.
The Taliban, Islamic State and other militant groups operate in Afghanistan and have carried out major attacks in and around the capital.
The National Directorate of Security (NDS) said on Sunday it had detained seven Islamic State members in the eastern city of Jalalabad, including a man believed to be in charge of planning urban area bombings.
An NDS statement said the group planned to target a gathering of Afghan security forces or tribal elders in the eastern province of Nangarhar, where Islamic State has carried out a number of attacks this year.
Suicide bomber vests, weapons and explosives were also seized.
Afghan and Taliban negotiators have been meeting in Doha since Sept. 12 hoping to agree on a ceasefire and a power-sharing deal. But they have been bogged down on procedures even before discussing their agenda.
Violence has risen despite the talks and the Taliban have rejected calls for a ceasefire.
Taliban fighters on Saturday launched attacks in the central province of Bamiyan in the bloodiest clash in the area, considered one of the safest in the country, since the start of the 19-year war.
Clashes continued for two days, with nine police killed and the Taliban suffering heavy casualties, Latif Azimi, spokesman for the Bamiyan provincial governor, said.
A Taliban statement said their fighters clashed with a convoy of security forces and that 30 Afghan commandos were killed.