The process would hinder efforts to win formal U.S. recognition of World War I-era killings of Armenians as genocide, said Ken Hachikian, head of the Armenian National Committee of America.
After decades of hostile relations, Turkey and Armenia last month agreed to establish normal diplomatic relations and reopen their border lands. The deal still must be ratified by the parliaments of each country.
More than 1 million Armenians died in forced marches and massacres during and just after World War I in conflicts with armies of the Ottoman Empire, Hachikian told an audience in Pasadena, Calif., Thursday.
Turkey, the successor state of the Ottoman Empire, long has denied genocide is an accurate description of the conflict, Hurriyet Daily News reported Saturday.
The agreement reached last month would "reduce the Armenian genocide from a crime against all humanity" to a simple, and unacceptable, bilateral dispute, Hachikian said.