As the U.S. braces for more conflict with Iran, Tehran says it is backing further away from a landmark 2015 deal to limit its development of nuclear weapons.

The state announced Sunday that it would not follow a key guideline of the agreement following the U.S. killing of its top general, Qasem Soleimani, on Thursday. Iran said it will not abide by the deal’s caps on the number of uranium enrichment centrifuges it can operate.

The announcement is only the latest blow to an international agreement that world powers hoped would reduce the chances of a nuclear standoff and normalize Tehran’s relations around the globe. Even after Trump announced he would withdraw from the deal in 2018, the other countries who signed on — China, France, Germany, Russia and the United Kingdom — aimed to keep it in place.

The latest spike in tensions follows decades of enmity between the U.S. and Iran. The timeline below outlines some of the major events in the U.S.-Iran relationship since the mid-20th century and how the nuclear deal into it.

— Timeline summaries by Reuters, with CNBC edits.

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