Mr Ahmadinejad said Iran was ready to shake "honestly extended" hands
China says placing sanctions on Iran is not the right way to resolve the controversy over its nuclear plans.
Foreign Ministry spokeswoman Jiang Yu called on all sides to "redouble diplomatic efforts" to persuade Iran to end its nuclear programme.
Her remarks came after Russia indicated it could soften its longstanding opposition to further sanctions.
Iran's nuclear ambitions are set to lead Thursday's nuclear proliferation debate at the UN General Assembly.
Tehran says its nuclear programme is for civilian use only but many Western states believe it is seeking to develop nuclear weapons.
Speaking in Beijing, Ms Jiang said: "We believe that sanctions and exerting pressure are not the way to solve problems and are not conducive for the current diplomatic efforts on the Iran nuclear issue."
Correspondents says Iran's oil and gas industries are likely to be affected if sanctions are strengthened, which could explain China's reluctance to back further restrictions.
Russia has already agreed to limited sanctions on Iran but has so far opposed any additions.
Quentin Sommerville, BBC News, Beijing
When Jiang Yu said that sanctions and pressure would not solve the Iranian nuclear issue, she was simply repeating China's stated policy of non-interference in another country's sovereignty.
China rarely votes "no" in the Security Council, but often abstains. However, Beijing has backed a number of resolutions that would open the way to sanctions against Iran, but did so with its nose firmly held. Sanctions don't work says China, they only victimise ordinary citizens. But is this sound principle or just smart business?
Trade between China and Iran is booming - it jumped by a third between 2007 and 2008. The United States and others accuse China of sanctions-busting and helping Tehran's weapons programme, something that Beijing has consistently denied.
On Wednesday, however, President Dmitry Medvedev said although they were rarely productive, sanctions were in some cases "inevitable".
"We need to help Iran to [make] the right decisions," he said, following a meeting with US President Barack Obama on the sidelines of the UN meeting in New York.
The move was welcomed by the White House. Spokesman Robert Gibbs said Russia's "willingness to play a constructive role is extremely important".
The BBC's diplomatic correspondent, Paul Reynolds, says Russia's apparent change of direction could have been influenced by the US announcement last week that it was dropping plans for an anti-missile defence shield close to Russian borders.
But exactly how far Russia might go is not yet clear, our correspondent says.
In his address to the General Assembly on Wednesday, Iranian President Mahmoud Ahmadinejad did not refer directly to the nuclear stand-off, but said Iran was ready to shake all hands "that are honestly extended to us".
US officials have stressed that Thursday's talks at the UN aim to create a "framework" for dealing with nuclear issues rather than focusing specifically on Iran.
"There is a deliberate effort here to focus on this issue comprehensively, and not use this meeting to focus on any specific country or problem," said the US deputy permanent representative to the UN, Alex Wolff.
However, Iran is expected to dominate the agenda.
Six world powers are preparing to hold talks with Iranian officials on 1 October that are expected to cover global nuclear disarmament.
Mr Obama is hoping for a united position among the group but analysts say that if the talks yield nothing, he wants to pursue tougher sanctions against Tehran.
On Wednesday, British Foreign Minister David Miliband said the six powers had agreed Iran must give a "serious response" to accusations against it.