Huge challenges ahead in talks with Iran: Obama

US President Barack Obama pledged there would be no more sanctions on Iran after the Islamic republic closed a first-step deal with the six major nations on its nuclear programme, but acknowledged "huge challenges" ahead for reaching a comprehensive agreement.

In remarks delivered at the White House, Obama hailed the deal as "an important first step toward a comprehensive solution" to Iran's nuclear programme, which the West suspects is a cover for making nuclear weapons, Xinhua reported Saturday.

"For the first time in nearly a decade, we have halted the progress of the Iranian nuclear programme, and key parts of the programme will be rolled back," Obama said, adding "Iran has committed to halting certain levels of enrichment and neutralising part of its stockpile."

According to the White House, Iran was committed to halting enrichment above five percent and neutralizing its stockpile of near-20 percent uranium by means of dilution or converting.

Obama acknowledged Iran's right to peaceful use of nuclear energy as he said, "We approach these negotiations with a basic understanding: Iran, like any nation, should be able to access peaceful nuclear energy."

In return for Iran's curbing of its nuclear programme, Obama said, "We will refrain from imposing new sanctions, and we will allow the Iranian government access to a portion of the revenue that they have been denied through sanctions."