German police investigating links between the military and the far right have seized weapons and explosives at the home of a special forces soldier.
The 45-year-old sergeant major in the elite KSK special forces command has been under investigation since 2017.
Reports say he had hidden a cache of weapons at his home in Nordsachsen in the eastern state of Saxony.
German military intelligence (MAD) said in January there were 592 suspected far-right cases in the army last year.
In March, officials said they had identified 27 people as far-right extremists. The KSK, considered the most secretive unit in the army, is seen as a particular problem.
It has some 1,000 soldiers trained for crisis situations such as freeing hostages abroad and 20 of them have reportedly come under investigation. Germany's Spiegel website says action has been taken against nine of them.
Defence Minister Annegret Kramp-Karrenbauer promised further investigation of possible extremist networks and said it was clear there was no place for anyone in the armed forces who acted "in a radical way".
The military's far-right problem emerged in 2017. Inspections were ordered on all military barracks when Nazi-era memorabilia was found at two of them. Many of those suspected of far-right links are thought to be sympathetic to Germany's main opposition AfD party.
The man arrested on Wednesday has also been under investigation since 2017 and he is suspected of arms violations. "So far, ammunition, explosives and weapons have been made safe. The soldier involved has been arrested and is currently being questioned by the authorities concerned," said defence officials.
An army officer called Franco A, who was accused of impersonating a Syrian refugee, is due to go on trial for planning a far-right attack.