US Secretary of State John Kerry said on Wednesday he is confident Barack Obama will be able to get Congress to approve a nuclear deal with Iran after the US president acknowledged lawmakers will have the power to review an accord with Teheran.

"Looming large is the challenge of finishing the negotiation with Iran over the course of the next two and a half months," Kerry said after arriving in Germany for a Group of Seven foreign ministers' meeting in the northern city of Luebeck.

"Yesterday there was a compromise reached in Washington regarding congressional input. We are confident about our ability for the president to negotiate an agreement and to do so with the ability to make the world safer," he added.