US Secretary of State Hillary Clinton has called for a high-level conference on Afghanistan at the end of March.
Solutions to the situation in Afghanistan can only be found if the countries involved, including Iran, meet, she said.
Mrs Clinton was speaking at a meeting of Nato foreign ministers in Brussels, where the alliance agreed to resume high-level contacts with Russia.
She will meet Sergei Lavrov, her Russian counterpart, later on Friday.
Russia welcomed the Nato decision, which comes six months after it froze contacts over the conflict between Russia and Georgia.
Mrs Clinton stressed Afghanistan, which she called "Nato's biggest military challenge", was a concern for both Russia and the West.
Afghanistan is Nato's biggest challenge, Mrs Clinton said
"If we move forward with such a meeting, it is expected that Iran would be invited as a neighbour of Afghanistan," she said.
French Foreign Minister Bernard Kouchner said that he hoped Iran would attend such a meeting, but noted that Tehran had failed to attend recent French talks on Afghanistan.
"I hope Iran will be here this time," said Mr Kouchner.
BBC diplomatic correspondent Jonathan Marcus says Nato remains central to the trans-Atlantic relationship but it is facing a critical challenge in Afghanistan, where failure could call into question its whole credibility.
On Friday, Mrs Clinton will hold talks with Russian Foreign Minister Sergei Lavrov.
The US is hoping that Russia will help secure new and safer supply lines for Nato troops in Afghanistan. Russia's help is also crucial in engaging Iran and curbing its nuclear plans.
Today's visit may be dominated by... Russia but Afghanistan remains the trickiest subject
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