Iran vowed on Monday to retaliate "ferociously" against any attack by the United States and reiterated warnings of a regional conflagration in response to President Donald Trump's threat of limited strikes.
The bellicose rhetoric from Tehran and Washington came as both sides worked to reach a deal on Iran's contentious nuclear programme in indirect talks due to restart in Switzerland on Thursday.
As Iran faces US pressure backed by a build-up of military force in the Middle East, university students have started the new semester with anti-government protests, reviving slogans from nationwide demonstrations that peaked in January and were met with a deadly crackdown.
Trump last week said he was weighing a limited strike if Iran did not cut a deal, but Tehran's foreign ministry reiterated Monday that any strike, even limited, "would be regarded as an act of aggression".
"And any state would react to an act of aggression... ferociously, so that's what we would do," ministry spokesman Esmaeil Baqaei said at a briefing in Tehran.
Iran has said it would be ready to deliver a draft proposal for an agreement on its nuclear programme to mediators in coming days, with Trump saying on Thursday that Tehran had at most 15 days to make a deal.
Iran insists its nuclear programme is for civilian use, but the West believes it is aimed at building an atomic bomb.
While Iran has taken anything beyond the nuclear issue off the negotiating table, Washington also wants to discuss Tehran's missiles and its support for militant groups in the region.
The two countries concluded a second round of indirect talks in Switzerland last week under Omani mediation and were due to continue on Thursday.
Iranian deputy foreign minister Kazem Gharibabadi said the talks were "a new window of opportunity", but warned of the risk of a regional conflict if his country was attacked.
"The consequences of any renewed aggression wouldn't remain confined to one country and responsibility would rest with those who initiate or support such actions," Gharibabadi said at the Conference on Disarmament in Geneva, calling on other countries to "take meaningful steps to prevent further escalation."
The risk of conflict has caused mounting fear in Iran and spurred other countries to take precautionary measures.
Agence France-Presse