The United Kingdom may be complicit in Gaza war crimes, according to a British diplomat who has resigned over the issue.

Mark Smith, who was second secretary at the UK's embassy in Ireland, said in his resignation letter: "Each day, we witness clear and unquestionable examples of war crimes and breaches of international humanitarian law in Gaza perpetuated by the state of Israel."

He said the fact that the UK has supplied weapons to Israel while "senior members of the Israeli government and military have expressed open genocidal intent" means the British government could be held legally responsible.

"I can no longer carry out my duties in the knowledge that this department may be complicit in war crimes," he added.

As examples of potential crimes, he highlighted Israeli soldiers taking videos of colleagues "deliberately burning, destroying and looting civilian property".

Israel has insisted its activities in Gaza are legal and in measured response to an Oct 7 attack in which more than 1,200 Israelis were killed.

The authorities in Gaza have said at least 40,000 people in the territory have been killed in the nine months that have followed, prompting the International Criminal Court to issue an arrest warrant for Prime Minister Benjamin Netanyahu for alleged war crimes.

Smith said he used to oversee arms export licenses while working in the British government's Middle East and North African Department, and that arms exports to Israel must stop immediately.

"There is no justification for the UK's continued arms sales to Israel and yet somehow it continues," he wrote. "I have raised this at every level in the organization, including through an official whistleblowing investigation, and received nothing more than 'thank you we have noted your concern'."

He said UK ministers' claims that the UK carefully controls arms exports "is the opposite of the truth".

Smith later told the BBC: "When you look at what constitutes a war crime, it's actually quite clear — even from what you see in open source on the TV — that the state of Israel is perpetrating war crimes in plain sight."

Sky News quoted a Foreign Commonwealth and Development Office spokesperson as saying the UK fully complies with international law.

"We have made clear that we will not export items if they might be used to commit or facilitate a serious violation of international humanitarian law," the spokesperson said.

Analysis by the Campaign Against Arms Trade claims the UK has exported more than 576 million pounds ($747 million) of weapons to Israel since 2008.

UK Foreign Secretary David Lammy ordered a review of those arms sales after the Labour Party was elected to govern the country on July 4. The review is ongoing.