Yukio Takasu, Japan's ambassador, said Mottaki used the gathering to reiterate Iran's position that it has the right to peaceful uses of nuclear energy.
But he indicated that there had been no concrete outcome following the dinner.
"We are not here to negotiate, we are here to exchange frank general ideas," the ambassador said.
"There was no talk about sanctions. What is important is that most security council members are here."
The US, which sent Alejandro Wolff, its deputy ambassador to the UN, said the gathering was an opportunity for Iran to show the council that it is "prepared to play by the rules".
A US official, speaking to the Reuters news agency before the dinner, said Washington decided to take part because the invitation also indicated Iranian officials are prepared to "meet their obligations".
"Iran has been offered many opportunities to prove the peaceful nature of its nuclear programme," the official said.
"This meeting is another indication of the lengths the Iranians are going to make their case.
"They clearly recognise that the ongoing efforts in the security council and elsewhere are isolating them and doing them harm."
Tehran reached out to the 15 security council members, despite stating that sanctions would not prevent it from pursuing its nuclear ambitions.
Mahmoud Ahmadinejad, Iran's president, said earlier this week at the UN that new sanctions would permanently damage relations between the US and Iran.
"Sanctions cannot stop the Iranian nation. The Iranian nation is able to withstand the pressure of the United States and its allies," he said.
"While we do not welcome sanctions, we do not fear them either."
The US, Britain and France have been pressing for a fourth round of penalties on Iran for its refusal to halt a key part of its nuclear programme that they say could be used to make weapons.
Iran says it only wants the technology to produce nuclear energy.