Support for human rights in Iran is more important than a nuclear arms deal, according to a former German diplomat.
Wolfgang Ischinger, who has served several chancellors, said concessions to the government in Tehran appeared to be a “slap in the face” to anti-government protesters.
Talks on reviving the 2015 nuclear deal between Iran and world powers have stalled for months.
Iran’s relations with the West have taken a turn for the worse as sanctions were imposed in response to repression of human rights protesters.
The UN said thousands have been arrested and hundreds killed during protests that are now in their fourth month.
Mr Ischinger, former chairman of the Munich Security Conference, said a revived nuclear deal could embolden the Iranian government at home.
“A negotiated text has been on the table for a while, but Tehran has so far shown no signs of accepting this offer and switching off its enrichment centrifuges,” he wrote in newspaper Handelsblatt.
“In the current situation, therefore, any western deference to the regime in Tehran would surely feel like a slap in the face to Iranians fighting for their freedom.”
Protests in Iran — in pictures
Mr Ischinger said the draft nuclear deal between Iran, the US, China, Russia, Britain, France and Germany should remain on the table.
But he called for tougher EU sanctions “without regard to the nuclear deal”, to show solidarity with protesters and punish Iran for supplying drones to Russia.
The West should “lay down a marker that people bravely protesting at risk of their lives will not be left in the lurch”, he said.
Britain and the EU signed off on more sanctions this week linked to the arms deal with Moscow.
The US said last month that the nuclear deal, formally the Joint Comprehensive Plan of Action, was not a priority while the Iranian protests continue.
Iran was committed under the JCPOA to limiting its nuclear enrichment in exchange for sanctions relief.
Since the US withdrew and reimposed sanctions in 2018, Iran has openly stockpiled and enriched uranium beyond what the JCPOA allows.
Tehran said its nuclear activities are peaceful but the UN’s nuclear watchdog said it cannot verify this until its inspectors are given more access to Iranian facilities.