First Iraq & Syria are different, number of players in Syria is no comparable with Iraq which all these have their own agendas ... i.e. while Turkey cooperates with Iran and Russia in Sochi it doesn't hesitate a moment to welcome the airstrike and says it wasn't enough :
“We are not surprised but we are disappointed. Although this is a good step, it is too little, too late. There was some hope that Trump would be different than [former President Barack] Obama and take the bull by the horns. It seems like this is just an opportunity for the Trump administration to distract the American public's attention. Not much will change for us in northern Syria.”
They still seek regime change. But the same Turkey that welcomed the US airstrike is fighting Kurds in north that are allied with the US. Therefore in this current intertwined complex scene in Syria which in a small fireworks could trigger next world war we need to be careful and cautious, let them be happy with these temporary airstrike. the goal is retaking all areas back and then going eastwards.
And the main Q regarding responding the US is do Americans seek direct confrontation with Iran in Syria? recent attack showed nor Iran nor Russia were attacked directly and everything was coordinated .. so it's better to just focus on those whom openly admits:
Israel Admits to Striking Syria: 'It Was the First Time We Attacked Live Iranian Targets'
With the US:
Iranian-Backed Group Threates To Attack US-Led Collation Forces And Bases In Syria
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On April 6, the Iranian-backed Baqir Brigade announced in an official statement that its units will begin conducting military operations against the US-led coalition and the US-backed forces in Syria. The brigade added that the US-led coalition bases in Syria are “within the range of its fire” and called on the civilians to stay away from these bases.
The Iranian-backed force was formed in Aleppo governorate in 2012 by two brothers named “Khalid al-Hassan” and “Abu al-Abass” of the well-known Arab tribe of al-Bakara. The two brothers reportedly fought alongside Lebanese Hezbollah during the 2006 Israeli-Lebanese war.
In 2015, the Baqir Brigade joined the Syrian National Defense Forces (NDF) and hundreds of fighters of the al-Bakara tribe joined its ranks. Baqir Brigade fighters participated in the battles against ISIS in Aleppo and Deir Ezzor governorates.
The Baqir Brigade came to the spot light when the US-led coalition killed dozens of its fighters during its airstrikes on the Syrian Arab Army (SAA) positions east of Deir Ezzor city on February 8. Back then, the commanders of the brigade and the leaders of the al-Bakara tribe vowed to take revenge from the US-led coalition.
Syrian opposition sources reported that the military capabilities of the Baqir Brigade had increased after it had recevied advanced weapons and loads of ammunition from Iran.
Local observers believe that the Baqir Brigade has means and the motivation to conduct serious attacks against the US-led coalition, unlike other “resistance movements” that had been recently formed in eastern Syria.
US creates 'no-man zones' at its bases in Iraq following Shia militias threats: report
ERBIL, Kurdistan Region (Kurdistan 24) – An Iraqi official on Wednesday claimed the US Army had taken precautionary measures at its bases in Iraq after continuous threats by the Iranian-backed Hashd al-Shaabi militias against American military presence in the country.