Angela Merkel has said antisemitism is a problem in Germany and the country has a historical responsibility to face up to the growing threat of far-right populism both at home and abroad.

Speaking after European elections where nationalists made gains and her Christian Democratic Union party (CDU) lost support, the German chancellor said “spectres of the past” meant the country always had to be vigilant.

“Germany … will not uncouple itself from developments we see all over the world, we see this in Germany as well,” she told CNN. “But in Germany they always have to be seen in a certain context, the context of the past, which means we have to be that much more vigilant than others.”

Her comments came just days after Germany’s ombudsman for antisemitism, Felix Klein warned German Jews not to wear kippahs in public after a spate of racist attacks.

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“We have always had a certain amount of antisemites among us,” Merkel said in the interview. “Unfortunately there is to this day not a single synagogue, not a single day care centre for Jewish children, not a single school for Jewish children that does not need to be guarded by German policemen.”

She added: “Unfortunately over the years we have not been able to deal with this satisfactorily ... but we have to face up indeed to the spectres of the past.”

An outdoor exhibition of photographs of Holocaust survivors by the German-Italian artist Luigi Toscano in Mainz, western Germany, is currently under police protection. Speaking after portraits in Vienna, Austria, were slashed and daubed with swastikas for the third time this month, Toscano described the vandalism as “the worst possible scenario … These survivors trusted me when I took their photos and now their pictures have been defaced.”

On Tuesday the UN’s human rights office condemned the attacks on the exhibition, which has been to 13 countries, and expressed concern “about the rise in antisemitic incidents taking place in a number of European countries and the United States”.

Facebook Twitter Pinterest Luigi Toscano stands near vandalised pictures of Holocaust survivors in Vienna. Photograph: Alex Halada/AFP/Getty Images

Merkel’s critics claim her decision to let almost 1 million refugees into Germany in 2015 contributed to a rise in support for the far right, in particular of the rightwing populist Alternative for Germany (AfD), but she defended her policy once again in the interview.

She said the best way to deal with immigration after humanitarian crises such as those in Syria and Iraq was not to “close ourselves off from each other”, but instead to be more vigilant to make sure that refugees were “adequately cared for”.

Merkel said it was a mistake for mainstream parties to cede power to populists and, due to Germany’s Nazi past, it was morally obliged to keep teaching the lessons of history.

“We have to tell our young people what history has brought over us, and others, these horrors,” she said. “It’s why we’re for democracy, why we try to bring about solutions, why we always have to put ourselves in the other person’s shoes. Why we stand up against intolerance, why we show no tolerance towards violations of human rights … The task has become harder but it needs to be done.”

Merkel was speaking after her party’s worst result in a national poll, and amid speculation she is being advised to return to the helm of the Christian Democrats.

Since giving up her position as party chairwoman in December to Annegret Kramp-Karrenbauer, who has frequently been referred to as her chosen successor, the CDU has had a rocky ride in the polls.

Kramp-Karrenbauer’s popularity is currently 20 points below that of Merkel, and the chances of success for Merkel’s notional ally Manfred Weber in the race to be the next president of the European commission are uncertain.

Consequently there have been widespread suggestions that Merkel has been asked to step up again. After a period of silence, she has given two high-profile interviews in quick succession, to the German newspaper Süddeutsche Zeitung, which was shared with the Guardian, and CNN.