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BERLIN — As foreign powers weigh further efforts to rein in Iran’s nuclear program, the German chancellor, Angela Merkel, is sounding markedly more determined about imposing tougher sanctions on the government in Tehran.

The shift — a potentially fraught move given the strength of Germany’s business dealings with Iran and the interest in preserving them during a recession — came about, diplomats and analysts say, after the Iranian authorities cracked down on protesters who charge that Mahmoud Ahmadinejad stole the presidential election in Iran in June. Mrs. Merkel, who grew up in Communist East Germany, was the first foreign leader to demand a new vote and to condemn the violence, speaking out well ahead of others, including President Barack Obama.

Iran — with its nuclear program and its domestic political turmoil — looms large on the global diplomatic agenda as leaders gear up for the United Nations General Assembly later this month. On Wednesday, senior diplomats from the United States, Europe, Russia and China met in Frankfurt to weigh the next step in years of fruitless efforts to curb what Iran insists is a civilian nuclear effort.

Twice in the past week, Mrs. Merkel has called for a much tougher stance if the Islamic Republic does not comply with international agreements and halt its uranium enrichment program.