By Kasra Naji
Iran targeted an Iraqi base hosting US troops to avenge the assassination of Gen Qasem Soleimani.
The defence secretary says "we know what we hit", after the first military action under Joe Biden.
How Mohsen Fakhrizadeh's murder "throws a monkey wrench" into Iranian relations with the US.
By Massoumeh Torfeh
Research Associate, LSE & SOAS
By Barbara Plett Usher
BBC State Department correspondent
By Paul Adams