DUBAI (Reuters) - Any communication between Tehran and Washington about U.S. citizens detained in Iran has been conducted via the Swiss embassy that handles U.S. interests rather than through direct contact, Iran’s foreign ministry spokesman said on Sunday. Saeed Khatibzadeh was reacting to remarks on Sunday by White House national security adviser Jake Sullivan, who said the United States had begun to communicate with Iran over Tehran’s detention of U.S. citizens. “This news is not true as stated and there is no direct dialogue between Iran and the United States in any field,” Khatibzadeh said, according to Students News Agency ISNA. Earlier a news website quoting an unnamed source said: “Iran’s government has not discussed American prisoners with Washington. All messages have been exchanged through the Swiss embassy in Tehran.” Switzerland represents U.S. interests in Iran because Washington and Tehran have no diplomatic ties. “Our priority is the release of Iranian prisoners in the United States,” Khatibzadeh said. Iran’s elite Revolutionary Guards have arrested dozens of dual nationals and foreigners in recent years, mostly on espionage charges. Rights activists have accused Iran of using them as bargaining chips, something Tehran denies. Tehran has repeatedly said it is ready for a full prisoner exchange with the United States. It says Iranians detained in the United States, mostly for breaking sanctions, are being unjustly held.