US Secretary of State John Kerry has lauded the Iranian people who voted in the country's presidential election for their "courage".
However, Mr Kerry said in a statement that the US remains "concerned about the lack of transparency in the electoral process, and the attempts to censor members of the media, the internet and text messages".
He continued: "President-elect Rouhani pledged repeatedly during his campaign to restore and expand freedoms for all Iranians. In the months ahead, he has the opportunity to keep his promises to the Iranian people.
"We, along with our international partners, remain ready to engage directly with the Iranian government.
"We hope they will honor their international obligations to the rest of the world in order to reach a diplomatic solution that will fully address the international community’s concerns about Iran’s nuclear programme".