Reuters dateline, Wed Jan 13, 2016 1:55am EST: “Iran’s Revolutionary Guards question U.S. sailors, dismiss talk of prompt release” Quoting,

“If, during the interrogation, we find out that they were on an intelligence gathering mission, we will treat them differently,” Guards spokesman Ramazan Sharif said in an interview with Tasnim news agency.”

This is the possibility considered in U.S. Sailors Held by Iran, with Iran’s diplomatic corps,  the voice of civil government,  contradicted by a religious voice, in this case a military force,  the IRG (Islamic Revolutionary Guards).

It has been suggested that the IRG, which has evolved into a complete military-industrial complex that controls a huge portion of Iran’s economy, has become more powerful than the theocracy. So if the U.S. sailors are detained, the origin of the detention has these possibilities:

• The detention of the American sailors past the expected release time originates with the IRG, who are dissatisfied with the nuclear deal.
• It originates with the hard line theological faction, of whom Yazdi is the preeminent representative.
• It  is collusive between the two.

Yazdi is aging, yet fit, and  recently ascendant in the Council of Experts. There are concerns for Supreme Leader Khameni’s health. It is a typical pattern of the aging autocrat to attempt to fortify the system against change, such as the election of a more liberal Supreme Leader.

This provides the background for Yazdi’s instigation. But it remains speculation without human intelligence, which is very hard to come by.