UPDATE — this extends our earlier coverage: Iran Brands New US Sanctions 'Economic Terrorism' as China Refuses to Join Pressure Campaign

Washington rolled out what officials call its toughest-ever sanctions package against Iran, trailed since mid-August as an "economic D-Day," according to CNN and Israel Hayom.

Oil prices fell as markets awaited the new measures, according to Anadolu Ajansı.

Iran warned of "earthquake-like" retaliation as the sanctions took effect, according to The Independent. The Islamic Revolutionary Guard Corps said it has prepared contingency scenarios to evade the new sanctions, according to Asharq Al-Awsat.

What to watch: which targets the sanctions name, the substance of Iran's promised retaliation, and whether the IRGC's evasion claims hold up.