US President Donald Trump on Sunday vowed “major retaliation” if Tehran launches attacks to avenge the killing of Iranian military commander Qasem Soleimani, ratcheting up fears of a spiralling conflict. Trump, speaking on Air Force One on his way back to Washington, also said he would impose “very big sanctions” on Iraq if it follows through on a parliament vote in support of US troops being expelled from the country amid anger over the death of Soleimani in a drone strike near Baghdad’s international airport.