Why did Iran deliberately avoid US casualties in Iraq missile attack?

Iran is believed to have deliberately avoided US military casualties during retaliatory missile strikes on bases housing American troops in Iraq, following the US killing of an Iranian general, according to US and European government sources familiar with intelligence assessments.

The sources, speaking on condition of anonymity, said on Wednesday, January 8 the Iranians were thought to have targeted the attacks to miss US forces to prevent the crisis from escalating out of control while still signalling Iranian resolve in response to the US killing of Iranian commander Qassem Soleimani in Iraq last week.

A source in Washington said overnight that early indications were that there were no US casualties following the strikes on the Al-Asad airbase and another facility in Erbil. Other US officials declined to comment.

'They wanted to respond but almost certainly not escalate' 

Iran was believed to have tried to hit certain parts of the bases to minimize casualties and especially to avoid US fatalities, three sources said. This assessment included some intelligence from inside Iran confirming the nature of the attack plan, they said. "They wanted to respond but almost certainly not to escalate," one of the US sources said.

The White House did not immediately respond to a request for comment. Iranian Foreign Minister Mohammad Javad Zarif said Tehran took "proportionate measures" in self-defence and did not seek war with the United States. The US President Donald Trump, who ordered the drone strike that killed Soleimani in Baghdad on Friday, gave an initial response to the Iranian missile attacks, saying on Twitter: "All is well!"