MAKING a deal with Iran will be difficult, U.S. Secretary of State Marco Rubio said during a visit to the Hungarian capital Budapest on Monday (February 16) because the country is led by clerics and Iran "make policy decisions on the basis of pure theology".

Rubio, who also serves as Trump's national security adviser, was on the second leg of a two-day tour of central Europe, visiting Slovakia and Hungary, whose conservative leaders have warm ties with Trump and are critical of the European Union.

The U.S. and Iran renewed negotiations earlier this month hoping to tackle their dispute over Tehran's nuclear program, which Washington, other Western states and Israel all believe is aimed at building nuclear arms. Tehran denies this. 

Rubio spoke as Iran's foreign minister met with the UN nuclear watchdog's chief in Geneva on Monday, ahead of the talks, with few clear signs of compromise from either side amid a U.S. military buildup.

Washington, which joined Israel in a wave of air strikes on Iran in June, has ordered a second aircraft carrier strike group to the Middle East in the latest showdown with Tehran, in addition to other warships and aircraft that have already been deployed.

Washington has sought to expand the scope of talks to non-nuclear issues such as Iran's missile stockpile. Tehran says it is only willing to discuss curbs on its nuclear programme in exchange for sanctions relief and won't accept zero uranium enrichment. It says its missile capabilities are off the table.