Russian president Dmitry Medvedev said in an exclusive interview with "Good Morning America" that he would consider withdrawing from the nuclear disarmament treaty he and President Obama signed last week, should the U.S. missile defense program in Europe create an "imbalance."
In an interview with ABC News' George Stephanopoulos, Medvedev said the two countries negotiated specific language, or a "formula," in the preamble of the new START treaty that states there is an "interconnection between the strategic offensive arms and missile defense."
"So if those circumstances will change, then we would consider it as the reason to jeopardize the whole agreement. That doesn't mean that because of that rule, if the American side starts to build up the missile system the treaty would automatically lose its power," Medvedev said.
"[If] the other party radically multiplies the number and power of its missile defense system, obviously that missile defense system is indeed becoming a part of the strategic offensive nuclear forces, because it's capable of blocking the action of the other side. So an imbalance occurs, and this would be certainly the reason to have a review of that agreement," Medvedev said.
This issue has long been a sticking point in negotiations between the two countries and Medvedev said should his country feel the missile defense program is a threat, then he would pose the question about a "premature end" to the agreement, but said he hopes that it would not come to that.
Following the signing Thursday of the treaty, which would reduce America's and Russia's nuclear arsenals by a third over seven years, Obama told Stephanopoulos that he is confident the Russians would not withdraw.
"We were firm, and are now absolutely confident that this in no way impedes our ability to move forward on the missile defense program, that's designed not to target Russia," he said in the ABC News interview.
CLICK HERE to read the full transcript of the interview.
Following 16 meetings and phone calls with President Obama, Medvedev said he considers him a "comfortable partner" and says he finds it "interesting" to meet with him.
"The most important thing that distinguishes him from many other people -- I won't name anyone by name -- he's a thinker, he thinks when he speaks," Medvedev said, but would not say who he was speaking about because he didn't want to offend anyone.
The Russian president said he found his American counterpart to be knowledgeable and a good listener, something he said was a good quality in a politician.
"There was no instance in our meetings with Mr. Obama where he wasn't well prepared for the questions. This is very good. And after all, he's simply a very pleasant man with whom it's a pleasure to deal," Medvedev said.
Ever since Medvedev, the handpicked successor of previous President Vladimir Putin, was elected in March 2008, questions have been raised about whether he or Putin, currently the Russian prime minister, is really in charge of the country.
Medvedev told Stephanopoulos that he found that question "annoying" and is "tired" of answering it.
"The decision is taken by the person who is designated to do it by law. If you consider the questions of foreign and domestic politics, the defense, the security, this is only the president. And nobody else," Medvedev said.
The president said despite having differing opinions on issues, he and Putin have a good professional and personal relationship.
"And how does the relationship work between Mr. Obama and Mr. Biden? They also sometimes speak [about] different things. They even have different backgrounds, different biographies, and probably a different set of opinions about the world and its situation. But it does work," Medvedev said.
In an exclusive interview last week, Obama told Stephanopoulos that he and Medvedev agreed that they should implement sanctions if Iran continues to develop its uranium enrichment program in pursuit of a nuclear weapon.
"I think it's an enormous shift and a signal that Russia, like the United States, recognizes that unless we can get all countries to start abiding by certain rules of the road, and right now, our biggest concerns are obviously Iran and North Korea," Obama said.
Medvedev told Stephanopoulos that the Iranian nuclear program is not transparent and must be carefully monitored. Should sanctions be implemented, Medvedev said, they need to be effective and smart because often they do not work.
"They should not lead to humanitarian catastrophe, where the whole Iranian community would start to hate the whole world," Medvedev said.
The Russian president shot down the notion of a crackdown on Iran's petroleum trade, an idea that many in Congress support.
"If we're talking about energy sanctions, I'll tell you my opinion. I don't think on that topic we have a chance to achieve a consolidated opinion of the global community on that. ... Sanctions should not be paralyzing. They should not cause suffering," Medvedev said.
Last month two female suicide bombers from the Caucasus region killed 40 people in a bombing in the Moscow subway.
Medvedev said it was a "tragic story," calling one woman a child because she was only 17.
"In order to fight such activity, you have to change the psychology of the people. You can create normal life conditions in the Caucasus. You have to destroy all of those who came here for terrorism. Those people are infiltrating through the borders," Medvedev said, referring to terrorists coming from Afghanistan and Pakistan.
Medvedev said Russia faces the same threat the United States does, and said he spoke to Obama about it last week.
"I told him 'Barack, the subways are in many places, and you should take care of the transportation.' This is a huge problem for our countries. And this is not just on the technological level. I'm ready to fully cooperate with our American partners," Medvedev said. "I know our American partners and the president are ready for the same. This is the struggle we'll have for a long time."