The consequences of a victory for extremist insurgents in Iraq are so "potentially catastrophic" that the possibility of sending British troops should not be ruled out, former defence secretary Liam Fox said.
Dr Fox said he understood the "extreme reluctance" of the UK and America to put western boots back on the ground but argued the option should stay on the table.
Iraqi security forces had been "pretty pathetic" in their response so far, he said, and it "remains to be seen" whether the country's prime minister Nouri al-Maliki could lead an effective response.
If that proved impossible, then western intervention would become irresistible, the Tory MP suggested.
London and Washington have ruled out putting troops on the ground as part of the response to the bloody territory grab by jihadists who have seized control of several key towns, including the second city, Mosul.
"There will be an extreme reluctance by any Western governments to do so but I don't think at the moment, given the potential consequences of Isis (Islamic State of Iraq and the Levant) success, that anything can be ruled out at this stage," Dr Fox told BBC2's Newsnight.
"The question in the coming days will be whether Maliki can rise up as a statesman at this late stage, whether the Iraqi military - given all the investment that has been made in their equipment and training - can fight back.
"That remains to be seen and then I think this situation will have to be watched very closely by the international community because the price of failure ... to confront and defeat Isis could be catastrophic and felt well beyond the region."
He added: "I do agree that it does look as though the Iraqi government are beginning some sort of fightback, notwithstanding the pretty pathetic efforts of their forces so far.
"We have seen them in the past being able to take on insurgents and they will hopefully be able to do so again."
He said Mr al-Maliki was "paying the price" for refusing to sign a status of forces agreement when Barack Obama withdrew American troops in 2011 - meaning none were able to stay to continue training and equipping Iraqi forces.