It also remained unclear what assurances, if any, China's President Hu Jintao had given Obama on Beijing's previously reluctant attitude towards the "biting" UN sanctions that the United States wants to impose on Tehran.
"My interest is not having a long drawn-out process for months," Obama said, appealing for nations to "move forward boldly and quickly," after pressing for a tough range of sanctions on Iran at the US-hosted nuclear security summit.
Asked a day after meeting Hu whether China would drop its reluctance to sign up for stiff sanctions, Obama did not reveal if he had been offered assurances by Beijing.
"Here's what I know. The Chinese have sent official representatives to negotiations in New York, to begin the process of drafting a sanctions resolution," Obama said.
"The United States is not moving this process alone," Obama said, noting that Russia had also agreed to join the effort in the Security Council.
Obama also defended the use of sanctions to punish Iran for not halting a nuclear program that the United States says is designed to produce nuclear weapons, a charge Tehran denies.
But he warned that "sanctions aren't a magic wand."
"What sanctions do accomplish is hopefully to change the calculus of a country like Iran so that they see there are more costs and fewer benefits to pursuing a nuclear weapons program."
Obama said that he had made a strong case that Iran's flouting of agreements like the Nuclear Non-Proliferation Treaty meant that the world would eventually have to draw a line in the sand.
"What I said to President Hu and what I've said to every world leader that I've talked to is that words have to mean something," Obama said. "There have to be consequences."
On Monday, a top White House official said Obama and Hu agreed during talks to jointly push for new nuclear sanctions on Iran.
"They are prepared to work with us," said Jeff Bader, Obama's top official responsible for East Asia on the National Security Council, referring to China.
"The two presidents agreed the two delegations should work together on sanctions."
However China, a veto-wielding member of the Security Council, undercut hopes for a consensus when it said sanctions were not a solution.
"China always believes that dialogue and negotiation are the best way out for the issue. Pressure and sanctions cannot fundamentally solve it," foreign ministry spokeswoman Jiang Yu said earlier.
Jiang said China backs a "dual-track strategy" consisting of continued dialogue with Tehran, but at the same time maintaining the possibility of sanctions if talks fail to halt sensitive nuclear work.
German Chancellor Angela Merkel said she was hopeful China would throw its support behind a fourth round of UN sanctions against a defiant Tehran.
Her optimism came as the United States reportedly pledged to keep China's oil imports flowing in case Iran retaliated by cutting off energy supplies to the Asian economic powerhouse.
"I see a positive development, even if it is moving slowly and we can't say whether it will lead to sanctions," Merkel told reporters, adding "I'm very hopeful."
"China is now part of the process, even though we can't say clearly what the outcome will be," she said on the sidelines of the landmark atomic summit which agreed to secure loose nuclear materials around the world within four years.
