The order came hours after Iran said it was within days of violating a central element of the landmark agreement — intended to curb its ability to develop a nuclear weapon — unless European nations agreed to help it circumvent the impact of tough American economic sanctions.

Context: The additional 1,000 troops come on top of 1,500 dispatched in May. The deployment, announced days after the U.S. blamed Iran for attacks on two oil tankers in the Gulf of Oman, will be used primarily for additional surveillance of Iranian activities and protecting American forces.

Analysis: Europeans blame Mr. Trump for pushing Iran into breaking out of an agreement that was working, as do China and Russia. And despite some calls for military action, Iran is betting that Washington will find few allies willing to escalate the confrontation, writes our national security correspondent.