CAIRO — As America talks to Iran, Saudi Arabia is lashing out against it.

The kingdom, Iran’s chief regional rival, is leading airstrikes against an Iranian-backed faction in Yemen; backing a blitz in Idlib, Syria, by jihadists fighting the Iranian-backed Assad regime; and warning Washington not to allow the Iranian-backed militia to capture too much of Iraq during the fight to roll back the Islamic State, according to Arab diplomats familiar with the talks.

Through Egypt, a major beneficiary of Saudi aid, the kingdom is backing plans for a combined Arab military force to combat Iranian influence around the region. With another major aid recipient, Pakistan, Saudi Arabia is also expected to step up its efforts to develop a nuclear bomb, potentially setting off an arms race in the region.

All this comes just a few weeks after the death of King Abdullah and the passing of the throne to a new ruler, King Salman, who then installed his son Mohammed, who is 29 or 30, in the powerful dual roles of defense minister and chief of the royal court.