"We have the greatest interest in the nuclear deal's survival and expect Iranian officials to do all they can so that this agreement remains alive," he said in an interview with Spain's El Pais newspaper published on Sunday, IRNA reported.
The nuclear accord, known as the Joint Comprehensive Plan of Action, has been fraying since last May when the United States unilaterally pulled out and reimposed sweeping sanctions on Tehran.
It came closer to the verge of collapse when the European parties failed to deliver on their promises to protect the Iranian economy, forcing Tehran to eventually take reciprocal action after a year by gradually scaling back its JCPOA commitments, according to Financial Tribune.
"We tell our Iranian friends that the best thing for them to do is not to allow this agreement to die," Borrell said, adding that it will be a "big mistake" if Iran takes steps that would lead to the deal's breakdown.
Iranian officials have declared repeatedly that all nuclear measures are revocable once the country's economic problems are properly addressed.
Borrell, a former Spanish foreign minister, assumed the post on Sunday as high representative of the European Union for foreign affairs and security policy and vice president of European Commission, headed by new President Ursula von der Leyen.
He has replaced Federica Mogherini, one of the most high-profile supporters of JCPOA.
"We continue to fully believe in the diplomatic and security value of … the nuclear deal with Iran. Yet it is no secret that the preservation of this agreement has become increasingly difficult," Mogherini said in her latest speech at the European Parliament plenary debate.
Europe has taken several steps to make up for the US sanctions, but none practically mitigated Iran's economic situation.
Among their key measures is a financial mechanism known as INSTEX (Instrument in Support of Trade Exchanges) that aims to facilitate trade with Iran, which has not been made operational, although it has been launched for nearly a year.
Recently, six EU countries announced their decision to join the mechanism, which bodes well for the practical operation of the system.