Tehran and world powers struck a deal last month on Iran's contested nuclear program, and yesterday Britain and Iran reopened their respective embassies after a break of several years.
Foreign Secretary Philip Hammond, who met Iranian President Hassan Rouhani in Tehran today, said the two countries shared common ground despite a "deep legacy of distrust."
He said they agreed on the need to defeat the Islamic State group, and to stop opium from Afghanistan reaching Europe.
Rouhani meanwhile dismissed any military option against his country's nuclear program as "ridiculous," after US President Barack Obama last week said force remained on the table to prevent Iran from getting a nuclear weapon.
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"These ridiculous expressions, slogans and irrelevant jokes damage the process of trust-building" between Iran and world powers, Rouhani said during his meeting with Hammond, according to the president's official website.
Obama has sought to address concerns among his fellow Democrats, who will need to support the nuclear deal to prevent the Republican-led Congress from derailing it.
The nuclear deal would curb Iran's nuclear activities and allow for greater international monitoring in return for sanctions relief.