Kata'ib Hezbollah, an Iraqi Shia paramilitary formation sponsored by Iran that lost its commander in the attack at the Baghdad airport that killed the Iranian general Soleimani, is giving an ultimatum to the Iraqi government that will result in the raised tensions and possible escalation of the sectarian violence.
Since the killing of the Iranian general, we have seen some rockets attacks on the military installation across Iraq but also some unknown planes pounding the positions of the Kata'ib Hezbollah, especially at the Syria-Iraq border.
The Trumps decision to take out Soleimani is celebrated by ISIS and we see their resurgence in the Deir ez-Zor province of Syria where they are attacking both the pro-government and Kurdish forces. With the Shia position weakened the Sunni extremists (including ISIS) will see that as an opportunity to regroup and attack again.
If Kata'ib Hezbollah attacks the US forces in Iraq, we'll see a Sunni uprising again and Iraq will be engulfed in a civil war with Iran supporting the Shia factions and the Gulf states (with USA?) fighting against them.