WASHINGTON – President Barack Obama said Tuesday he has told Russia that reducing Iran's pursuit of a nuclear weapon would in turn lessen the need for a U.S.-planned missile defense system in Eastern Europe that Moscow has opposed. But Obama said he sought no "quid pro quo" with Moscow. The new president also said it is time for the U.S. to "reset or reboot" its relationship with Russia, a nod to the increasingly tense relations of recent years. Answering questions at a picture-taking moment in his meeting with visiting British Prime Minister Gordon Brown, Obama was asked about a letter he sent to Russian President Dmitry Medvedev regarding a series of mutual security concerns, including U.S. plans for deploying U.S. missile defenses in Poland and the Czech Republic. "What I said in the letter is the same thing I've said publicly, which is that the missile defense that we have talked about deploying is directed towards not Russia, but Iran," Obama said. "That has always been the concern — that you have potentially a missile from Iran that threatened either the United States or Europe." Obama disputed a published report that said he characterized his letter as "quid pro quo" with Russia, which has opposed the missile defense system. He said it was simply "a statement of fact." He said lessening Iran's commitment to nuclear weapons "reduces the pressure for, or the need for, a missile defense system." But that, he said, does not diminish his own commitment to ensure that Poland, the Czech Republic or other NATO members enjoy full U.S. support with respect to their security. More broadly, Obama said he has had a good exchange with Russia's leadership. "I've said that we need to reset or reboot the relationship there," Obama said. "Russia needs to understand our unflagging commitment to the independence and security of countries like a Poland or a Czech Republic. On the other hand, we have areas of common concern." The president said he wants a constructive U.S.-Russia relationship "based on common respect and mutual interests." Medvedev said he had talked with Obama over the phone and exchanged letters with him, but added that there was "no talk about some kind of trade-off, or quid pro quo." "No, issues haven't been put that way, it would be unproductive," he said at a news conference Tuesday, which followed talks in Madrid with Spanish Prime Minister Jose Luis Rodriguez Zapatero. Medvedev reaffirmed a strong opposition to the previous U.S. administration's plan to deploy a battery of missile interceptors in Poland and a related radar in the Czech Republic, saying the move would hurt security in Europe. Medvedev said that Russia was encouraged by Obama's administration's readiness to discuss Moscow's complaints. "Our American partners are ready to discuss this problem, and that's already positive," he said at a news conference. "Several months ago we were hearing different signals: The decision has been made, there is nothing to discuss, we will do what we have decided to do." "Now I hope the situation is different," Medvedev added. "But no one is linking these issues to some kind of trade-offs, particularly on the Iranian issue. We are already working in close contact with our U.S. counterparts on the Iranian nuclear issue." Obama and Medvedev are expected to meet at the G-20 economic summit of advanced and developing nations in London next month, according to senior administration officials. U.S. officials emphasized that "we will continue to consult with the Czechs and Poles as we move forward with decisions on missile defense." That message was an obvious attempt to ease fears among those two U.S. allies — former Soviet satellite states — who are deeply invested in the missile defense system as an assurance of American backing against a resurgent Russia. The administration has previously hinted that the policy on the missile defense shield that former President George W. Bush fiercely advocated was open to reassessment. And Defense Secretary Robert Gates said he told Russian leaders a year ago that if there were no longer an Iranian missile threat there would be no need for the system in Europe. "I don't think at all that this is trying to put the Russians on the spot," Gates said during a Pentagon press conference. "I think it is trying to reopen a dialogue and say we are open to talking with you about how we address this problem." Gates also pointed to a Bush administration offer to Russia to sign on as a partner in the program. "The reality is that the missiles that the Iranians are testing can reach a good part of Russia, as well as Eastern Europe and part of Western Europe. These missiles cannot reach the United States at this point." Secretary of State Hillary Rodham Clinton, speaking at a news conference in Jerusalem while on a Mideast tour, said that "we are at the beginning of the engagement with Russia on behalf of this new government." "We have a very broad agenda also, what we have said specifically in regard to missile defense in Europe is that it has always been intended to deter any missiles that might come from Iran," she said. __ AP White House Correspondent Jennifer Loven, AP Military Writer Anne Gearan and AP reporter Ben Feller contributed to this report.