MOSCOW (Reuters) - Russian Deputy Foreign Minister Sergei Ryabkov said on Friday it was “extremely troubling” that U.S. President Donald Trump was raising questions that had been settled when an international deal on Iran’s nuclear program was signed, RIA news agency reported. Ryabkov was quoted as saying that Russia sees its main task now as preventing the Iran nuclear deal from collapsing. He called on all sides to stay committed to the deal, the news agency reported. 