(Reuters) - Iran and the United States have been informed that $6 billion in frozen Iranian funds were transferred to accounts in Qatar, a source said, triggering a carefully choreographed swap on Monday of five detainees each between the two arch foes.

Iran's Foreign Ministry spokesperson Nasser Kanaani said the funds, which had been frozen in South Korea, would be in Iran's possession on Monday so the deal mediated by Qatar during months of talks could go ahead.

There was no immediate public U.S. comment.

"Both parties have been notified by Qatar that all $6 billion has been transferred from Switzerland to bank accounts in Qatar," the source briefed on the matter told Reuters.

"A Qatari aircraft is on standby in Iran waiting to fly five soon-to-be released U.S. citizens and two relatives to Doha on Monday morning."

Under the deal, the five Americans with dual nationality are expected to leave Tehran and head to Qatar's capital Doha and then from there fly to the United States.

In return, five Iranians detained in the U.S. will be released. The Iranian Foreign ministry spokesperson said two would return to Iran while two would stay in the U.S. at their request. One detainee would join his family in a third country, he added.

The deal, first made public on Aug. 10, will remove a major irritant between Washington and Tehran, although the two sides remain deeply at odds over issues ranging from Iran's nuclear ambitions and its influence around the region to U.S. sanctions and America's military presence in the Gulf.

South Korea's Foreign Ministry had said on Monday it was working with all parties on the deal "to ensure smooth progress of all procedures so that it will be resolved once and for all."