Dhaka, June 23 -- The European Union's top diplomat Kaja Kallas on Sunday called for de-escalation and a return to negotiations after the United States joined Israel's war with Iran by striking the country's nuclear sites.Kallas said that Iran must not be allowed to develop a nuclear weapon, describing the possibility as "a threat to international security" - but stressed that Brussels remained committed to diplomacy, at a flashpoint moment for the Middle East."I urge all sides to step back, return to the negotiating table and prevent further escalation," Kallas wrote on X, adding that EU foreign ministers will discuss the situation on Monday.Top diplomats from the bloc's 27 nations were already due to gather in Brussels for talks on a ra...