Angela Merkel began her short statement by offering her condolences to the families of the victims of Tuesday's attacks in Brussels, in which more than 30 people were killed. "Let me express my condolences, both on behalf of the German government and on my behalf personally," Merkel said.

Merkel said she had spoken to Belgian Prime Minister Charles Michel to offered Germany's solidarity, and that her cabinet would meet tomorrow morning to discuss "in depth" the response to the Brussels attacks. She added that she was in constant contact with her security forces.

The chancellor also struck a defiant note against the attackers.

"The murderers of Brussels are terrorists who have no regard for the precepts of humanity," the chancellor said. "The murder scene of Brussels reminds us above all that the perpetrators are enemies of all the values for which Europe stands today, and which we as members of the European Union believe in - and, particularly on this day, with great pride - the values of freedom, democracy, and peaceful co-existence as self-confident citizens."

"Our strength is in our unity, and that is how our free societies will prove themselves stronger than terrorism," she added.

German police tighten security

Germany's federal police reported that they had increased security on the borders with Belgium, France, the Netherlands and Luxembourg, as well as at airports and railway stations following Tuesday's attacks in Brussels.

In a press statement released shortly after midday, the police also said that officers on the ground had been provided with "extra protective equipment suitable for the location."

The police did not want to give further details on the measures taken, but following last November's machine gun attacks in Paris, German security forces drew up an action plan on how to respond to a terrorist attack in a neighboring country, which was leaked to "Der Spiegel" magazine.

According to the plan, armed police are to patrol key points at German stations, special units alerted, and surveillance of known extremists is to be stepped up.

Meanwhile, the German Foreign Ministry told travelers in Brussels to "move around only with increased awareness and caution."

A spokesman for the ministry said the embassy in Brussels was "working urgently to find out whether Germans had also been affected by the explosions."

But Interior Minister Thomas de Maiziere said there were was no information yet on whether there had been any German victims - or if the attackers had had any connections to Germany. "We don't even know if the situation is finished yet," he said at a press conference in Berlin. He added that German security forces were in close contact with their Belgian counterparts.

Germany's national rail operator, Deutsche Bahn, has temporarily suspended all trains to Belgium's capital, and both of Berlin's airports announced that all flights to Brussels were canceled for the day. In addition, Tegel airport said it was shutting its observation deck.

Abdeslam's German connection

Security forces are pursuing the possibility that Salah Abdeslam, the alleged "Islamic State" (IS) ringleader arrested in Brussels last Friday, was planning attacks in Germany, according to a newspaper report.

Berlin's "Tagesspiegel" reported that an anonymous "senior security expert" had told the newspaper that Abdeslam belonged to an IS network that was "explicitly" trained for attacks in Germany and other countries. The newspaper's report contained no other direct quotes from the source.

The speculation is based on a trip that Abdeslam took to the southern German city of Ulm in early October 2015, six weeks before the terrorist attacks in Paris that he helped organize.

Last week, Belgian police found a location between two Ulm hotels stored in the GPS of a car hired by Abdeslam in early October. German state broadcaster SWR reported on Sunday that in one of these hotels the police found a booking under the name of "Munir Ahmed A.," which French authorities have linked to an ID card with the name "Amine C." found during a police raid on a Brussels flat last week.

Abdeslam, Brussels-born but with French nationality, was the subject of a long manhunt following the Paris attacks on November 13. His 31-year-old brother Brahim Abdeslam blew himself up near the city's Bataclan club, where one of the attacks took place.

Shock and solidarity

In the wake of the attacks in Brussels, various German politicians have expressed their shock and offered condolences via Twitter, including Steffen Seibert, the spokesman for Chancellor Angela Merkel, who wrote on Twitter that "the disgusting attacks in Brussels will leave us standing together: solidarity with the victims and determination against the terrorists."

Justice Minister Heiko Maas wrote: "Shocking news from Brussels. These are simply barbaric acts. Our sympathy goes to the families and friends of the victims."

Peter Altmaier, the chief of staff to Chancellor Angela Merkel, tweeted: "Unbelievable. The terrorists must never win! Europe's values are stronger than hate and violence! Total solidarity with Brussels and the EU."

There was also a more surprising post from the insurgent populist right-wing party Alternative for Germany, whose deputy leader, Beatrix von Storch, was in Brussels at the time of the attack in her role as a member of the European Parliament.

"Best wishes from Brussels," von Storch wrote on her Facebook page. "We have just left the parliament. Helicopters circling. Military moving in. Sirens everywhere. Apparently many dead at the airport and the central railway station. But it's nothing to do with us."

Several users and media outlets accused von Storch of tastelessness.