The Ministry of Defence said two RAF Tornados fired Brimstone missiles at an armed pick-up truck and transport vehicle west of Baghdad.
It is the second time UK forces have engaged IS since the Westminster parliament authorised involvement in the international military campaign last week.
At a fringe event at the Tory conference on Tuesday night, Work and Pensions Secretary Iain Duncan Smith insisted the Cabinet, including Liberal Democrat members, unanimously believed IS would have to be dealt with in Syria. Labour’s reluctance was behind the coalition government’s decision only to seek approval for air strikes on forces in Iraq, he added.
“The reality, I have to be honest with you, is that it is a Labour issue, it is an issue for the Labour Party. We need to carry the House of Commons on these things and so the answer here is that Labour decided that, frankly, this was not a step they wanted to take, so it conditions what we are doing.
“To be honest with you, there was absolute unity around the Cabinet table, including the Liberal Democrats as well, all basically saying the same thing – that the complete package is ultimately having to deal with Isil [another name for IS, meaning Islamic State of Iraq and the Levant], not Isil in one place.”
Defence Secretary Michael Fallon yesterday said two Tornado GR4s from RAF Akrotiri in Cyprus were tasked to assist Kurdish troops under attack by IS.
They destroyed a heavy weapons post and pick-up armed with a mounted machine gun.
Meanwhile, the wife of British hostage Alan Henning earlier issued a renewed plea for IS to release her husband.
The IS extremists have also released a third propaganda video appearing to feature British photo-journalist John Cantlie.
The 5½-minute clip, shows Mr Cantlie sitting at a desk dressed in the orange outfit worn by other IS hostages.
Mr Cantlie, who looks calm and appears to be reciting a script, describes himself as a “long-term prisoner” and goes on to criticise US President Barack Obama’s strategy of attempting to defeat IS fighters using air strikes.
Of the latest air strikes, the MoD said: “Following yesterday’s strikes on the Isil terrorist organisation, Royal Air Force aircraft have seen further action overnight.
“Two Tornado GR4s from RAF Akrotiri conducted an armed reconnaissance mission in support of Iraqi government forces west of Baghdad.
“They were tasked to examine a location suspected of being used as an Isil command and control position. At the scene they were able to identify Isil activity and two vehicles, one an armed pick-up truck.
“Four Brimstone missiles were used to conduct a precision attack on the vehicles. Initial analysis indicates that the strikes were successful.”