BISHKEK, Kyrgyzstan -- Iranian President Mahmoud Ahmadinejad lashed out at a U.S. missile-defense plan Thursday, saying it threatened countries in a regional grouping that has emerged as a powerful bloc countering American interests.

Mr. Ahmadinejad spoke at the summit of the Shanghai Cooperation Organization, which includes Russia, China and four ex-Soviet countries in Central Asia. Iran has observer status in the organization. Russia has vehemently objected to U.S. plans to place elements of a missile-defense system in Poland...