Berlin police have arrested two men suspected of recruiting fighters and gathering equipment and finance for the Islamic State in Syria, as security forces across the country intensify their investigations into suspected terror groups.

Following the recent attacks in Paris and the thwarting on Thursday of a terrorist plot in Belgium, 250 officers simultaneously raided 11 addresses across the German capital.

The raids were part of a lengthy investigation over several months into a small terror cell based in Berlin. But it is understood the investigations were accelerated following the events in Paris and Belgium.

The two men, of Turkish origin, were identified as Ismet D, a 41-year-old who is suspected of heading the organisation and of recruiting mainly Turkish and Russian nationals to fight in Syria, and Emin F, 43, who is believed to have been responsible for the cell’s funding. According to Germany’s privacy laws, they can only be identified according to their first names.

As security officials sought to assuage fears that an attack on German soil was imminent, saying any such threat remained “abstract”, they stressed that the Berlin terror cell had been planning attacks in Syria, not inside Germany.

Martin Steltner, a spokesman for Berlin prosecutors, also said the arrests were “unrelated to the recent attacks in Paris or raids in Belgium”.

“This is just a coincidence,” he said.

In a further apparently unrelated raid, police in the city of Wolfsburg, 125 miles (200km) west of Berlin, arrested a 26-year-old German-Tunisian former Volkswagen worker believed to have fought in Syria. In a video of his arrest seen by the tabloid newspaper Bild, Ayub B, wearing a black baseball cap and with a cloth bound around his face, stretched his right hand into the air and shouted: “Allahu akbar”.

A high-ranking police officer told Spiegel Online that Germany was in a higher than usual state of alert and that police feared copy-cat incidents. “The situation is tenser than usual,” he said. “We fear that the incidents in France could act like a combustive agent on the scene in Germany.”

Germany’s Federal Criminal Police Office or BKA has long been warning that a growing number of lone offenders are active in the country. In an operating review released on Monday, the BKA said young German Muslims were vulnerable to being swept along by the mission statements of terror cells. As a result German police have been taking a decisive stance against jihadists in Germany since the Paris attacks.

On Saturday, a 24-year-old convert to Islam, identified as Nils D, who is believed to have spent a year in Syria with Isis and lost friends from Germany in the fighting there, was arrested in Dinslaken, North Rhine Westphalia.

On Monday evening police arrested an Islamist called Gabriel K in Cologne after a special commando stormed his flat. Also a convert, Gabriel is accused of voicing a threat during a telephone call to carry out a terror attack. He was later released.

On Tuesday, police at Dusseldorf airport acted on an international arrest warrant and seized Irfan D, a 55-year-old Dutch-Turkish citizen, who is believed to have operated as a fundraiser for the Islamic Movement of Usbekistan. The US is seeking his extradition.

Police searched several flats in Pforzheim in Baden-Würrtemberg on Thursday, suspecting several residents of preparing a serious act of violence.

German authorities are aware of around 500 to 600 young men who have been to fight in Syria and Iraq. The police have said they would need more than 6000 further officers to be able to properly monitor them.

The government is currently trying to introduce legislation allowing authorities to confiscate the national ID cards of suspected jihadists, with which they are currently able to travel as far as Turkey, and replace them with different ID cards to prevent them from leaving the country.