Rory Stewart has accused his leadership rivals of poor taste after a Tory source suggested he was a “suicide bomber” candidate attempting to clear the path for Michael Gove.

In an interview with the Guardian, the international development secretary, who previously served as a governor in Iraq during the Iraq war, said he found the trope offensive and that he was in the Tory leadership race because he believed he could win.

Stewart pledged on Tuesday that he would deliver Brexit by convening a citizens’ assembly of 500 members of the public who would be paid to sit seven days a week to determine an outcome that parliament could support, but has said he would not countenance a no-deal exit.

Stewart said he believed the negative briefings were coming from Boris Johnson’s supporters and suggested he was being targeted because of growing support for his candidacy.

“The fact these guys are using the word ‘suicide bomber’, that is something uncomfortable for me as someone who has been around Iraq and Afghanistan. I can’t think of who else, a leading figure in British politics, who might use such a phrase, ‘suicide bomber’,” he said – a nod to Johnson, who once described Theresa May’s Brexit plan as a “suicide vest”.

Stewart, whose campaign so far has consisted of shaky handheld videos talking to voters in various London boroughs, said other candidates “are beginning to realise they are not as nimble as they thought on social media, they are not that good at getting out on the street … I think it is a sign I am getting a bit of edge and putting some pressure on them.”

Stewart, who spent Monday and Tuesday in London suburbs, will head to Wigan on Wednesday. He said he aimed to conduct his entire “guerrilla” campaign via social media videos, intending to cover huge distances across the streets of the UK in the coming weeks to speak to voters, inspired by his walk across Afghanistan in 2002.

The MP is currently the only candidate of the 11 declared so far who has explicitly ruled out a no-deal Brexit, a view that puts him at odds with about 66% of Tory members, according to polling.

Instead he hopes to deliver Brexit via a citizens’ assembly, which he said he would convene on day one of entering No 10 and would pay a jury of 500 UK citizens to work a seven-day week to find a Brexit consensus that parliament would respect.

Stewart said he was inspired by the assembly that was convened around the abortion debate in Ireland. “I have a lot of confidence that we are one of the most educated and articulate populations on Earth and that if we had a citizens’ assembly they would be able to do what parliament has failed to do: step back, put party politics aside and look at a sensible resolution to this,” he said.

He said the outcome would be known by 31 October and would deliver Brexit more swiftly and securely than a candidate prepared to risk no deal.

“You need a Brexit deal to last for 40 years – the danger of revoke or no deal is that you end up in a very unstable situation. The issues are set up as very binary but actually in Ireland they broke it down to a whole series of different questions,” he said.

The assembly could potentially discuss a second referendum but Stewart said he believed they would reach the conclusion that it would be too divisive, leaving many issues unsolved.

“I’ve been an advocate for a pragmatic, moderate Brexit. My position would have been acceptable to most people who voted remain just after the referendum but positions have hardened,” he said. “A lot of people now want to reject the result of the referendum entirely. I did not feel that in the first weeks and months after the referendum.”

Stewart said he believed the House of Commons was unable to take on a similar role because of party divisions. “I have fantasised about locking members of parliament in a room, bringing in an international mediator, forcing them to take public evidence sessions from expert panels and groups for eight or nine hours a day, setting up a voting system to force them to come to a resolution,” he said.

“But the more I have looked at it, the more it is obvious to me that is not going to happen. Even before the second vote, I came across colleagues on both Labour and Conservative benches who didn’t understand or want to understand some pretty straightforward things, like what is the difference between the single market and customs union.

“Fundamentally, there is not a huge gap between me and Lisa Nandy [the Labour MP for Wigan who has advocated against a second referendum]. The problem is we are in different political parties. It’s so, so deep.”

Stewart’s chances of the leadership look wafer-thin, with just two declarations from supportive MPs, and with the Conservative membership appearing to overwhelmingly back either Johnson or Dominic Raab.

He said he believed it was a “stressful time for MPs” but with about 140 still to declare he insisted he could make up ground. “People are afraid of the party splitting, they are afraid of getting deselected. They are looking at the candidates and thinking, which one can get Brexit done and beat Jeremy Corbyn and reunify the country – that is the way they keep their seat.”