Robert Jenrick has doubled down on his widely criticised claim that UK special forces are “killing rather than capturing terrorists” after a Conservative Party leadership rival accused him of misunderstanding the law of armed conflict.

The frontrunner in the race to replace Rishi Sunak defended as “absolutely correct” his assertion that the British military is taking lethal action because of fears that European laws would free any detained assailants.

Asked on Tuesday whether he could back up the claim, he insisted he could not “elaborate on particular cases” and instead cited comments made by ex-defence secretary Ben Wallace to the Telegraph.

Mr Wallace told the newspaper last year that Britain was unable to render people across borders, meaning “we are more often than not forced into taking lethal action (rather) than actually raiding and detaining”.

Leadership rival Tom Tugendhat said he was “extremely concerned” at Mr Jenrick’s remarks, while fellow contender James Cleverly urged him to justify his statement in media appearances on Tuesday morning.

Repeatedly asked whether he knows that special forces are killing terrorists instead of capturing them, Mr Jenrick told BBC Radio 4’s Today programme: “As Ben Wallace has said in that (Telegraph) interview, decision-makers are being asked to make decisions which they might not ordinarily make – for example, to call in a drone strike and take lethal action in that way.”

It was put to the former immigration minister that he is unable to back up his claim, to which he replied: “Of course I’m not going to elaborate on particular cases because these things, these cases are not things that any minister or foreign minister can speak about.”

He denied he could have chosen his words more carefully, insisting “the point I was making was absolutely correct”.

The European Convention on Human Rights (ECHR) is “forcing decision-makers to make decisions which they might not ordinarily make,” he suggested.

Mr Jenrick drew condemnation from across the political divide over his statement in a promotional video for his leadership bid that special forces are “killing rather than capturing terrorists because our lawyers tell us that if they are caught the European court will set them free”.

Former Conservative attorney general Dominic Grieve described the clip as “one of the most astonishing videos I have ever seen posted by a Conservative MP, let alone a candidate for the leadership”.

A Labour source said: “Robert Jenrick’s ludicrous attempt to politicise our special forces shows you how far the Tories have fallen. He should apologise. Our brave servicemen and women deserve better than this.”

Asked whether he agreed with the claim, shadow security minister Mr Tugendhat told Sky News: “No, I don’t. I think what he said is wrong and I’m afraid demonstrates a fundamental misunderstanding of military operations and the law of armed conflict.

“I’m extremely concerned that such words should not be seen in any way to encourage people to take any action other than surrender to British forces when asked to do so.”

The British military always abide by international humanitarian law, the law of armed conflict ... Our military do not murder people

Former foreign secretary Mr Cleverly said: “You’re going to have to ask Robert to justify that statement. That’s not something which I have heard.

“That’s not something which I’m comfortable kind of repeating.

“The British military always abide by international humanitarian law, the law of armed conflict.

“We have, I was about to say some of the most… no, we have the most professional military in the world. Our military do not murder people.”

In the Telegraph article cited by the leadership frontrunner, Mr Wallace criticised the international human rights framework, bemoaning the “lunacy” of Britain being “unable to arrest people in countries whose police forces are unacceptable.”

But he stopped short of calling for the UK to leave the ECHR – a move supported by Mr Jenrick.

Nicknamed “Robert Generic” when first elected to the Commons in 2014 for his apparently moderate politics, Mr Jenrick has gradually moved to the right of the Tory Party.

The MP for Newark resigned as a minister last December, claiming legislation designed to revive the former Rwanda deportation policy did “not go far enough”.

He insisted on Tuesday that his values “haven’t changed” but that his time as a minister, particularly in the Home Office, led him to the conclusion that “the British state isn’t working in the interests of the British people”.

“I saw that we were not able to secure our borders and to keep the public safe, which to my mind is the most basic duty of our country,” he said.