German police commando units have arrested two people in Berlin who are suspected of planning an attack, a police spokesman said this afternoon.
Police first searched a mosque in western Berlin before finding them at separate location in the south of the capital.
Police have sealed off an area where a suspicious car was found.
German police said they used sniffer dogs, but that no weapons or explosives had so far been found.
The raids, involving special forces police, targeted first an Islamic cultural centre in western Charlottenburg district, and then a building in the southern suburb of Britz.
"In connection with this threat, two men were detained in #Britz," tweeted Berlin police, adding in another message that "during a search of their vehicle, a suspicious object was found".
The men were aged 28 and 46, reported national news agency DPA.
Police also tweeted that in Britz, "some houses are currently being evacuated as a precaution for the forensic examination of the suspicious object".
Bild newspaper reported that police had acted on a tip-off that an attack was being planned, as European police forces are on high alert following the recent attacks in Paris.
Meanwhile, Belgian authorities have reduced the terror alert in Brussels, five days after it was raised to the highest possible level.
The reduction to Level 3 - serious, a possible and probable threat - from Level 4 - a very serious, "imminent" threat - brings the capital into line with the rest of the country.
There were no immediate details on what basis the agency reduced the threat level, with the national security council of top government officials set to decide on the consequences at a meeting later today.
The alert level was raised early Saturday after the government warned of a "serious and imminent threat" of attacks in the capital similar to the Paris atrocities that left 130 people dead on 13 November.
The city was locked down with armed police and troops patrolling near deserted streets and the metro system completely shut down, while schools stayed shut on Monday and Tuesday.
Belgian Prime Minister Charles Michel had said on Monday the threat level would remain at its highest until 30 November, but that it would be reviewed constantly.
Security alert at Great Mosque
Meanwhile, the Great Mosque of Brussels was evacuated and 11 people were decontaminated after a suspicious package containing white powder was found.
The mosque, the city's biggest, is located just a few blocks from the major EU institutions and many embassies and was cordoned off by police and firemen, some of them in white hazard materials suits.
Anne Wibin, a spokeswoman for the fire service, said eleven people, including two police offers, were decontaminated as a precautionary measure.
