Spanish police say they have arrested nine people suspected of planning a series of violent attacks for the anniversary of a divisive referendum.
The suspects are described as Catalan separatists by police sources, who say they plotted to strike on 1 October.
That will be the second anniversary of a Catalan independence referendum declared illegal by Spanish courts.
Bomb-making materials were found during the raids across the semi-autonomous region of Catalonia, police said.
The detainees belong to a group that has led recent protests, police added.
Known as the Technical Response Teams, they are seen as the most militant arm of the Committees for the Defence of the Republic (CDRs).
Police raided 10 addresses in Barcelona, Sabadell and Santa Perpètua de Mogoda at 05:00 local time (03:00 GMT) on Monday.
Computer hardware and documents were seized, police say, in addition to the arrests. They say they have not ruled out making further arrests.
The CDRs were created by Catalan separatists a month before the 2017 referendum to carry out its implementation.
Separatists say there has been no violence in their campaign.
On Twitter, the CDRs called for protests over the arrests, which it characterised as an act of repression by Spanish officials.
Catalonia’s unauthorised independence referendum two years ago – which saw the province attempt to unilaterally declare itself a separate state from Spain – led to an ongoing political crisis.
The region had its autonomy suspended for almost seven months by Madrid over the failed bid to break away.
There is also tension ahead of the verdicts for 12 Catalan separatist leaders who organised the drive for independence. They are on trial for sedition and rebellion – which they deny.