Relations between the United States and Russia soured in part because the Americans wanted to build the European Missile Defense system, Russian President Demitry A. Medvedev wrote in a letter to the editor of The Washington Post.

He provided the letter just as he was meeting with President Obama at a Group of 20 Nations summit meeting in London.

Medvedev wrote that “obstacles to good relations” should be removed, meaning that the United States should abandon plans to build the European Missile Defense system that Russia alleges would threaten its intercontinental ballistic missiles.

But Obama, in his European trip, said that Iran remains a threat. The U.S. president did not agree during his trip to abandon plans to build the EMD system.

The Post published that Medvedev letter March 31.