SOME $6 billion of Iranian assets in Qatar have become a key element for a planned prisoner swap deal between Tehran and the US, an Iranian official said today.

Nasser Kanaani made the comment during a news conference aired on state television, but the feed cut immediately after his remarks without explanation.

Iranian news agencies then reported, quoting Mr Kanaani, that the prisoner swap was set to be carried out on Monday. 

The announcement by Mr Kanaani comes weeks after Iran said that five Iranian-Americans are now under house arrest as part of a confidence-building move while Seoul allowed the frozen assets, held in South Korean won, to be converted into euros. 

That money was then sent to Qatar, which has acted as a go-between in negotiations between Tehran and Washington.

The swap unfolded amid a major US military build-up in the Persian Gulf, with the possibility of US troops boarding and guarding commercial ships in the Strait of Hormuz, through which most oil is shipped.

The deal has also already opened US President Joe Biden to fresh criticism from those, such as the Republican opposition, who say he is helping to boost the Iranian economy at a time when Iran poses a growing threat to US troops and their Middle Eastern allies.