Chris Coons, a US senator and a possible secretary of state in a Biden administration, said on Friday he would support returning to the 2015 Iran nuclear deal only if there were a path to limit Tehran's missile programme and its support for regional proxies.
The agreement, which US President Donald Trump abandoned in May 2018 before restoring related US sanctions, sought to restrict Iran's nuclear programme to prevent it from developing weapons in return for the easing of economic sanctions.
It did not, however, restrict Iran's ballistic missile programme nor Tehran's support for militias in Iraq, Lebanon, Yemen and Syria, which the US regards as destabilising to the Middle East and that threaten US partners in the region.
Asked if he would support a return to the pact, formally called the Joint Comprehensive Plan of Action, Mr Coons, a Delaware Democrat, told Reuters: "Not without some clear path towards addressing the missile programme and support for proxies."
President-elect Joe Biden, who will take office on January 20, said he would rejoin the deal if Iran first resumed strict compliance and would work with allies "to strengthen and extend it, while more effectively pushing back against Iran's other destabilising activities".
Saying that he was speaking for himself, Mr Coons said Washington would "need a path forward for limits on their missile programme and their support for proxies before I would support re-entering the JCPOA. These need to happen at the same time".
Returning to the deal would be complicated, and sketching out a way to a further agreement on restraining Iran's missile and regional activities would likely be even harder, not least because Iran is sure to demand something in return – if it were even willing to consider such constraints.