“We are very worried about the risk of a conflict happening by accident, with an escalation that is unintended really on either side,” said Jeremy Hunt, the British foreign secretary.
The Iranian government has not threatened violence recently, but last week, President Hassan Rouhani said Iran would walk away from parts of the 2015 nuclear deal it reached with world powers. Mr. Trump withdrew the United States from the agreement a year ago, but European nations have urged Iran to stick with the deal and ignore Mr. Trump’s provocations.
The high-level review of the Pentagon’s plans was presented during a meeting about broader Iran policy. It was held days after what the Trump administration described, without evidence, as new intelligence indicating that Iran was mobilizing proxy groups in Iraq and Syria to attack American forces.
As a precaution, the Pentagon has moved an aircraft carrier, B-52 bombers, a Patriot missile interceptor battery and more naval firepower to the gulf region.
At last week’s meeting, Mr. Shanahan gave an overview of the Pentagon’s planning, then turned to General Dunford to detail various force options, officials said. The uppermost option called for deploying 120,000 troops, which would take weeks or months to complete.
Among those attending Thursday’s meeting were Mr. Shanahan; Mr. Bolton; General Dunford; Gina Haspel, the C.I.A. director; and Dan Coats, the director of national intelligence.
“The president has been clear, the United States does not seek military conflict with Iran, and he is open to talks with Iranian leadership,” Garrett Marquis, a National Security Council spokesman, said Monday in an email. “However, Iran’s default option for 40 years has been violence, and we are ready to defend U.S. personnel and interests in the region.”