Chancellor Angela Merkel sought to reassure Germans on Saturday after her government alerted the country to a heightened terrorist threat, saying everything is being done to ensure people's security.

Merkel's interior minister, Thomas de Maiziere, raised Germany's security level Wednesday. He cited an increased threat from extremists but didn't give specific details.

"I think everything is being done to ensure the security of people in Germany," Merkel said on the sidelines of a NATO summit in Lisbon, Portugal. "We have a real threat from terrorism ... but we are determined not to be deprived of our free way of living by such threats."

Merkel's comments came after the weekly Der Spiegel reported, without citing sources, that an informer claimed to German authorities that al-Qaida planned a possible attack early next year on Berlin's Reichstag parliament building.

She had no comment on that, but the head of Germany's Federal Criminal Police Office called the report "highly speculative," the German news agency DAPD reported.

"There are no indications of specific places, people or moments," Joerg Ziercke said in Hamburg.