Trump Warns Iran to 'Get Serious Soon'; Rubio Acknowledges Unclear Negotiating Partner

President Trump warned Iran that negotiators 'better get serious soon, before it is too late,' signaling the April 6 deadline is firm. US Secretary of State Rubio acknowledged in a Friday statement that it remains unclear who will speak for Iran in any formal negotiations — a significant admission given the elimination of much of Iran's senior leadership. UK National Security Adviser Jonathan Powell secretly attended US-Iran nuclear negotiations in Geneva, per The Guardian — the first confirmed British presence in the talks. Iran's parliament speaker Ghalibaf has been in contact with US envoys Witkoff and Kushner (per Axios), representing the Iranian side given the degraded state of Iran's executive branch. Iran formally responded to Trump's 15-point plan, calling it 'one-sided and unreasonable.'