The accord, reached between Tehran and world powers in Vienna in July 2015, saw Iran drastically curb its nuclear activities. In return, nuclear-related Western and UN sanctions were lifted.
But writing in Friday's Guardian newspaper, Mr Salehi, head of Iran's Atomic Energy Organisation, said negotiating agreements with Western powers had been a 'mixed experience' for Tehran.
"Often, following some hard won engagement, some Western nations, whether distracted by shortsighted political motivations or the lucrative inducements of other regional actors, walk away and allow the whole situation to return to the status quo ante," he said.
Mr Salehi was writing against the background of increasing US Iran tensions since President Donald Trump came to power.
He said the nuclear deal could be saved but it would take concerted action and a clarification of Western security policy in the Middle East.
"For example, US arms sales to some traditional regional clients in the Middle East, and ostentatious, lavish arms purchases by the same regional actors just because of the abundance of oil wealth, are provocative," he said.
Trump has vowed to 'dismantle' the 'disastrous' nuclear deal and has ratcheted up US sanctions, calling for Iran to be isolated and throwing his weight behind Tehran's arch rival Saudi Arabia.
Last month, on his first foreign trip, Trump visited Saudi Arabia and promised its leaders access to $110 billion in weapons and training.
Mr Salehi called for engagement from all parties.
"We have, so far, taken a number of solid steps towards a constructive engagement aiming at common goals and objectives. Those steps could be strengthened further by genuine reciprocal gestures and actions. The moment of truth has arrived," he said.