WARSAW, Poland (AP) — The presidents of Germany and Poland met in Warsaw Thursday to celebrate the 30th anniversary of a key treaty between the two neighbors, focusing on the positive aspects of a sometimes wobbly relationship.

Germany's Frank-Walter Steinmeier held talks with Poland's Andrzej Duda, and attended a meeting with young people from both countries.

The two neighbors are at odds over the Nord Stream 2 gas pipeline linking Germany with Russia. Warsaw strongly opposes what it sees as a political tool for increasing Russian influence in Europe, while Berlin views it as purely a business project.

The presidents made no direct reference to the subject at a news conference following their first round of talks.

Steinmeier only said that Germany “takes criticism seriously and will make every effort to achieve reasonable solutions.”

He added that good Polish-German relations were “one of Europe's greatest successes in the past 30 years.”

The presidents also discussed plans underway for a memorial in Berlin to some 3 million Polish victims of the brutal World War II Nazi German occupation. Poland, which Germany invaded in September 1939 — triggering World War II — has been pressing for such a memorial.

Another issue both presidents mentioned was the rights of the German minority in Poland and the Polish minority in Germany.

The good-neighborly relations treaty was signed in 1991 — two years after Poland shed Moscow's dominance and embarked on forging its independent West-oriented policy.

One of the main goals was to put aside the long history of conflicts and warfare between the two countries. Berlin was a strong advocate of including Poland in Western structures such as NATO, which it joined in 1999, and the EU, which it joined in 2004.

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Geier Moulson in Berlin contributed to this report.

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