The prime minister replaced an experienced former general with Katz, who had been foreign minister and who staunchly supported Israel's right-wing government.
While Donald J. Trump is seen by many in Tehran as a disaster for their country, some hope he may be more open to negotiations for a second term as president of the United States.
Emergency service workers continued to search for victims of last week's flash floods as a national debate raged over who was to blame for the catastrophe.
Human rights groups said Reza Valizadeh, an Iranian-American journalist, was recently arrested in Iran, although the State Department did not confirm that he was the person detained.
A Scottish artist, he has said he believes there are "funny sides" to terrible experiences, including some he has drawn from his own moments of loss and difficulty.