US Secretary of State John Kerry on Wednesday "words are no substitute for actions" on the Iran nuclear issue and said it was too early to talk about easing sanctions on the country.

US Secretary of State John Kerry on Wednesday "words are no substitute for actions" on the Iran nuclear issue and said it was too early to talk about easing sanctions on the country.

Speaking ahead of marathon talks in Rome with Zionist Prime Minister Benjamin Netanyahu, Kerry said US sanctions on Iran could be revoked only once it is clear the country's nuclear program is peaceful.

"We do welcome the change of rhetoric, the change of tone, the diplomatic opening that the Iranians have offered," Kerry said, adding however: "We are adamant that words are no substitute for actions".

For any discussion over sanctions, he said: "We will need to know that actions are being taken which make it crystal clear, undeniably clear, failsafe to the world that whatever program is pursued is indeed a peaceful program."

At the same time he hailed the recent signs of openness in Iran following the election of President Sheikh Hasan Rouhani and said the country should now respect the same rules as other nuclear powers.

"No deal is better than a bad deal," he said, adding: "President (Barack) Obama has made it very clear he will pursue a diplomatic initiative, but with eyes wide open".

Nuclear talks between Iran and western powers are gathering steam after Iranian negotiators last week presented new proposal to the West aimed at ending the stand-off.