Lambrecht and her 21-year-old son Alexander flew from Berlin to northern Germany on board a Bundeswehr helicopter in mid-April, Business Insider reported, adding that the son had posted a picture of the flight on Instagram.

Lambrecht used the trip to visit troops in Stadum in the state of Schleswig-Holstein, before travelling on to the nearby island of Sylt for a brief Easter break with her son.

A defence ministry spokesman told AFP that Lambrecht did not breach any rules by bringing a family member along on the helicopter, and that Lambrecht "covered 100 percent of the costs" of his flight.

German media nevertheless questioned the wisdom of the move, with Der Spiegel weekly saying it "raised some eyebrows" and the Bild daily asking whether the holiday had been necessary at all in the middle of the Ukraine crisis.

Opposition lawmaker Thorsten Frei, from the centre-right CDU party, accused Lambrecht of confusing the German air force "with Lufthansa".

"Using the Bundeswehr military for private and partisan means is inelegant," he told Bild.

MP Reinhard Brandl, a defence policy spokesman from the CDU's Bavarian sister party, the CSU, said the timing of Lambrecht's vacation "was already borderline" given the war in Ukraine.

"That her son is now also boasting on Instagram that he was allowed to fly on a government helicopter to Sylt is the last straw," he told Spiegel.

Lawmaker Marie-Agnes Strack-Zimmermann from the liberal FDP, whose party belongs to the coalition government headed by Lambrecht's Social Democrats, said the decision to bring the son on the helicopter was "unusual".

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