Former German Chancellor Angela Merkel has warned that even if President Vladimir Putin made a “big mistake” by invading Ukraine, long-term isolation of Russia is not possible.

“There’s no excuse for this brutal aggression,” the 67-year-old said in an on-stage interview at a central Berlin theater on Tuesday as part of her tentative return to public life. While she has kept busy behind the scenes, this was her first public appearance in front of a larger audience since leaving office in December.

She spoke out about the Ukraine war for the first time last week, three months after President Vladimir Putin ordered the attack. She condemned Russia’s “barbaric war of aggression” and spoke of a “profound break” in Europe’s post-war history at a private event hosted by a labor union group.

Germany’s prospects have changed dramatically in the six months since he stepped down. Russia’s invasion of Ukraine has exposed Europe’s largest economy to a number of risks and raised concerns about her policies, including underinvestment in Germany’s defense and reliance on Russian energy imports.

Despite her lack of public visibility, Merkel has remained active behind closed doors. According to a person familiar with her schedule, she repeatedly called Putin’s office and spoke with the Russian leader about a possible cease-fire shortly after Russia’s invasion of Ukraine on February 24.

The dialogue was not a haphazard effort like Merkel’s predecessor Gerhard Schroeder’s March trip to Moscow. According to the person, who asked not to be identified because the discussions were private, Chancellor Olaf Scholz was aware of the calls and was regularly briefed on the results. According to the source, Putin stopped returning Merkel’s phone calls about six weeks ago.

When asked if she had met with Putin on Tuesday, she avoided a direct response, saying she would not do anything unless the government asked her to.

The event at the Berliner Ensemble theater, which was founded by Bertolt Brecht and is a short walk from Merkel’s private apartment, has been sold out for weeks, reflecting the former chancellor’s enduring popularity after her 16-year tenure ended. Merkel stated that she has been spending time on the Baltic coast and listening to audio books, and that she will not return to active politics, stating that she has “complete trust” in Germany’s current political leadership.

Merkel’s only other public appearance was in April to respond to criticism from Ukrainian President Volodymyr Zelenskiy, who accused Merkel of contributing to the invasion by blocking Ukraine’s NATO accession in 2008.

Her office issued a written statement defending her decision at the time and expressing support for all efforts to end the war by the current German government. On Tuesday, she outlined her reasons for opposing Ukraine’s membership in NATO, claiming that the country was not yet ready due to internal divisions and widespread corruption.

She went on to say that the move would have been a “declaration of war” for Putin, echoing Scholz’s concern about escalation. Despite NATO’s rejection, she stated that she has always supported Ukraine.

According to people familiar with the situation, Scholz has frequently sought Merkel’s advice. Former and current German leaders appear to have reached the same conclusion: Germany should support Ukraine in its fight against Russia, but avoid putting Putin in a corner.

Scholz has recently stated that he wants to prevent Putin’s victory in Ukraine, but he has not stated that he wants Ukraine to win. The less confrontational tone appears to be in keeping with Merkel’s cautious style.

When Putin annexed Crimea in 2014, she attempted to reach a diplomatic solution rather than risking military conflict. According to a person familiar with Merkel’s thinking at the time, Merkel was already concerned about the outbreak of a nuclear war if tensions escalated. Scholz has expressed concern about this.

She defended engaging with Putin during her tenure, citing the country’s size and nuclear arsenal, and warned of the risks of Putin forming an alliance with China if he becomes trapped.