BERLIN (Reuters) - Police arrested four suspected Islamists in dawn raids in Berlin on Wednesday as the German capital geared up for a long weekend of mass gatherings, capped by a joint appearance by Chancellor Angela Merkel and former U.S. president Barack Obama.

German Federal Police patrol next to a concrete barrier before the opening service of the German protestant church congress Kirchentag in front of the Brandenburg Gate in Berlin, Germany, May 24, 2017. REUTERS/Fabrizio Bensch

Police said the raids targeted a gang of armed drug smugglers and nine arrests had been made, four of which were men from the “violent Islamist” scene. None were linked to the Manchester bomb attack which killed 22 people on Monday.

However, a senior politician promised security would be reviewed in the wake of the attack, as the German capital braces for some 100,000 extra visitors over the next few days, but that plans were in place for any such eventuality.

“We’ll take another look, but our security plans are designed so we’re well prepared for events like that in Manchester,” Berlin’s interior affairs senator, Andreas Geisel, told RBB radio on Wednesday.

With the city hosting Germany’s football cup final, a mass religious meeting as well as Obama, huge crowds are expected throughout the spring weekend.

Memories are still fresh of the Berlin Christmas market attack last December, in which 12 people were killed, and flags hung at half-mast across Germany on Wednesday to express solidarity with Manchester after the attack.

Geisel said some 6,000 police will be deployed on Berlin’s streets over the Ascension Day long weekend, which begins with the German protestant church’s biennial four-day Kirchentag festival.

Security at events elsewhere in Germany over the long weekend would be adjusted following events in Manchester, interior minister Thomas de Maiziere said.

“We mustn’t focus exclusively on access controls,” he told Bild newspaper. “The Manchester events have shown that the situation at the end of the event have to be looked at carefully, when people leave the hall or stadium.”

Obama, a close ally of Merkel while he was in office, was due on Thursday to address crowds from the spot where his predecessors John F. Kennedy and Ronald Reagan stood when the city was on the front lines of the Cold War.

His visit, seen as lending a hand to Merkel’s campaign to be returned to office in September, will be followed on Saturday by the German Cup final, when Eintracht faces Dortmund.