The challenge for the administration in contemplating economic pressure is that it would be all but impossible to reassemble the international coalition that imposed draconian sanctions on Iran’s oil and banking industries — and drew Iran into negotiations that resulted in the agreement limiting its nuclear program.

Mr. Flynn pinned much of the blame for Iran’s aggressiveness on former President Barack Obama, saying his administration “failed to respond adequately to Tehran’s malign actions — including weapons transfers, support for terrorism and other violations of international norms.”

He also noted that Mr. Trump had criticized agreements between Iran and the Obama administration as “weak and ineffective.” During the campaign, Mr. Trump spoke of ripping up the Iran nuclear agreement, though his aides now say their focus is less on abrogating that deal than on constraining Iran’s behavior in the region.

In Yemen, for example, the Pentagon is considering stepped-up patrols and perhaps even airstrikes, aimed at preventing Iranian weapons from getting to the Houthis. In addition, Saudi officials are pushing for more support for their air campaign in Yemen, an administration official said. But officials said on Wednesday that there had been no change in the military’s posture.

While the Obama administration targeted Houthis and conducted airstrikes against forces aligned with Al Qaeda in Yemen, current and former officials say Mr. Obama was wary of deepening American support for the Saudi air campaign because of concerns about the accuracy of targeting and the large number of civilian casualties.

“Obama said all the time, ‘Aim before you shoot,’” said Derek Chollet, who served in the White House, the Pentagon and the State Department during the Obama administration. “Anytime there was one of these heated discussions, and people said, ‘We’ve got to do something,’ he said, ‘O.K., what does the intel say, and where will this take us?’”