Police and Sweden's security police Säpo carried out joint raids on several locations in northern Sweden and the Stockholm region early on Monday morning, the authorities said in a press statement.
Three suspects were arrested, and several other people were brought in for questioning.
The arrests were made in the suburb of Akalla north of Stockholm.
Säpo said they had been monitoring the suspects as part of their counter-terrorism work.
“Preparations for the suspected crime have been ongoing for some time, but at the moment there are no indications that an attack was planned over the coming days,” they said.
A spokesperson told TT the case had “international connections” but did not elaborate.
Citing unnamed sources, TT reported that all three suspects were from Uzbekistan. It also reported that at least one had been in contact with Rakhmat Akilov, who is currently on trial for the April 2017 Stockholm terror attack. The claims were not immediately confirmed by authorities.
The prosecutor and Säpo both declined to reveal any further information.
Sweden's terror threat level remains at three (“elevated level”) on a scale from one to five, where it has stayed since 2010, apart from a brief period in late 2015 when it was temporarily raised to four.