"We can confirm that we have received Iran’s response through the EU," the spokesperson said.
"We are studying it and will respond through the EU, but unfortunately it is not constructive."
The official's remarks follow an earlier statement attributed to Iranian Foreign Ministry spokesman Nasser Kanaani, who relayed to Reuters that Tehran's response was "constructive." Similar sentiments had also made by EU officials.
The exchange marks the latest in a series of back and forth contacts between US and Iranian negotiators working to find common ground on potentially resurrecting the Iran nuclear deal. Earlier in August, EU officials issued a "final text" to both the US and Iran for terms on limiting Tehran's nuclear advances while also providing sanctions relief.
The US exited the JCPOA during the Trump administration, when then President Donald Trump parted ways with the Obama-era agreement and accused Iran of breaking stipulations outlined in the deal. Trump followed up the move by launching a "maximum pressure" campaign against Iran. In turn, Iran has increased its levels uranium enrichment.