Iran has warned that it will face serious problems if it does not negotiate, according to President Donald Trump. The Iranian foreign ministry has condemned the U.S. seizure of an Iranian-flagged cargo ship, describing it as "piracy" and an "act of aggression" against Iran. The seizure was seen as a clear breach of the two-month U.s.-Iran ceasefire. Two top Iranian officials, likely to lead the team in possible new talks, have warned against negotiating under threat.