While U.S. and Russian officials denied a flat-out quid pro quo, Medvedev told the U.N. General Assembly that Obama's pivot on a missile defense plan long loathed by Moscow "deserves a positive response." Obama himself has said his missile decision may have spurred Russian good will as a "bonus."
"We believe we need to help Iran to take a right decision," Medvedev said after the two leaders met on the sidelines of the U.N. assembly.
The prospect of a unified U.S.-Russian stance on new sanctions would put Iran under added pressure to yield some ground on its nuclear program. Iranian President Mahmoud Ahmadinejad has taken a softer tone on many matters since arriving in New York for the U.N. meetings, emphasizing his interest in improving relations with the United States and expressing an openness to include nuclear matters on the negotiations agenda.
He has given no sign, however, that his country is willing to bargain away its nuclear program, which he insists is for peaceful purposes only.
"We have not actually changed our mind," Ahmadinejad told CBS Evening News anchor Katie Couric in an exclusive interview before his address to the U.N. "Our nuclear program will be pursued in accordance to international law."
Watch: Couric Questions Ahmadinejad on Nuclear Program
In his speech to the General Assembly on Wednesday night, or prospective sanctions.
"They have never really wanted to engage seriously on this issue," Walter Russell Mead, a Senior Fellow at the Council on Foreign Relations told CBS News senior White House correspondent Bill Plante. "I would be surprised if that changed."
Obama's chief Russia adviser, Mike McFaul, told reporters after the meeting with Medvedev that there was no deal with Moscow on missile defense and Iran. Pressed further, he said: "Is it the case that it changes the climate? That's true, of course. But it's not cause-and-effect."
A member of the Russian delegation, speaking on condition of anonymity under ground rules set by the Russians, said Moscow's final position on the question of imposing further sanctions would be determined, to a large extent, by Medvedev's consultations here.
The U.S. and Russia are among six countries that will hold talks in Europe next week with Iran over its nuclear ambitions. Obama wants to reserve the possibility of pursuing tougher sanctions if those meetings lead to no restraint by Iran in the weeks ahead. And yet Russia, which has strong economic ties with Tehran, has stood in the way of stronger action against Iran in the past.
In remarks to reporters with Medvedev at his side, Obama said both agree that negotiations with Iran are still the best approach.
"We also both agree that if Iran does not respond to serious negotiations and resolve this issue in a way that assures the international community that it's meeting its commitments, and is not developing nuclear weapons, then we will have to take additional actions and that sanctions, serious additional sanctions, remain a possibility," Obama said.
Medvedev told reporters that the intent is to move Iran in the right direction and to ensure that it does not obtain nuclear weapons.
"Sanctions rarely lead to productive results but in some cases are inevitable," he said through an interpreter.
Medvedev also mentioned that his government welcomed Obama's decision last week to scrap a Bush administration plan for a missile defense system to be based in Poland and the Czech Republic. He gave no indication that his remark about the sanctions on Iran was a diplomatic payoff for Obama's missile defense move.
Watch: New Approach on Missile Defense
In earlier Wednesday, Obama stuck to his two-pronged approach to Iran - acknowledging its right to the peaceful use of nuclear energy while warning of unspecified penalties if it veers onto the weapons path.
"We must insist that the future not belong to fear," he said.
Ahmadinejad spoke Wednesday evening.
The public rhetoric Wednesday suggested little improvement in the long-shot outlook for a diplomatic breakthrough next week when the U.S. will, for the first time, fully participate in European-led talks with Iran.
CBS News analyst Juan Zarate told Early Show co-anchor Harry Smith Thursday that it was very important that Medvedev had even mentioned the possibility of sanctions. However, Zarate cautioned that previous sanctions against Iran had been watered down severely in UN negotiations by the Russians and the Chinese, and there was not yet a clear indication that it wouldn't happen again.
Zarate also pointed out that, even if there is agreement among the U.S., Russia and China that new sanctions are necessary, those three nations may have different ideas on how quickly they should be put into force.
Secretary of State Hillary Rodham Clinton met Wednesday with her counterparts from Russia, China, Britain, France and Germany to prepare for the Oct. 1 meeting in Geneva. Afterward British Foreign Secretary David Miliband read a statement on behalf of all six countries saying they expect a "serious response" from Iran at the meeting. What happens after that, Miliband said, will be determined by the outcome of the meeting.
Ahmadinejad told The Associated Press on Tuesday that in Geneva he would ask to purchase enriched uranium for a research reactor. That could put the U.S. and its five negotiating partners in a bind. Until now, Iran has produced only low-enriched uranium not suitable for a research reactor. But it could use refusal of its request as a pretext to start producing highly enriched material.
In his speech Obama did not mention the Geneva talks, which fulfill a campaign pledge to engage adversaries. He framed the Iran issue as central to his broader push to strengthen international limits on the spread of nuclear weapons.
Obama singled both Iran and North Korea, which has made more progress than Iran in becoming a nuclear power, as countries that now are at a crossroads.
"Those nations that refuse to live up to their obligations must face consequences," Obama said.
The risk for Obama, in the case of Iran, is that the government will use the new talks to stall for time even as international patience wears thin. That is essentially what has happened with North Korea, which agreed at one stage to dismantle its nuclear weapons facilities but then balked and has since defied the will of the U.N. by conducting underground nuclear tests and test-launching missiles.
Obama came into office promising a more vigorous diplomatic effort with Iran, which also stands accused by the U.S. of supporting international terrorism, undermining Mideast peace efforts and secretly supplying arms to insurgents in Iraq and Afghanistan.
Obama has not ruled out the eventual use of military force to stop Iran, but his focus now is on diplomacy.
In the meantime, Iran is expected to continue expanding its capacity for enriching uranium, the building block of a nuclear weapon. Still, Ahmadinejad said Iran has no interest in nuclear weapons and favors a push for global nuclear disarmament.
"We are not pursuing a nuclear weapons program," he said in the AP interview.
The Iranian leader insisted that it is the United States that bears the greatest burden in nuclear disarmament. The U.S., he noted, possesses thousands of weapons, is the only country in history to have used them in war and refuses to promise never to initiate another nuclear attack.
Iran, he said, is "the wrong address" for delivering international pressure to pull back.
Obama, however, indicated that Iran needs to clarify its intentions and the nature of its nuclear work by cooperating more fully with the International Atomic Energy Agency, the U.N. agency that is supposed to monitor nuclear programs to ensure they are not used to make weapons.