Boris Johnson has condemned the Metropolitan Police for investigating Israel over alleged war crimes in Gaza.
Scotland Yard recently launched an appeal for witnesses to the conflict in the Middle East.
The force has erected posters at various British airports, including Heathrow, aimed at anyone returning from Israel or the Palestinian territories who has witnessed terrorism, war crimes or crimes against humanity.
The posters, written in Arabic and English, address “travellers who have been in Israel/Palestinian Territories”.
The Met said the posters had been put up to support a long running investigation into Israel by the International Criminal Court (ICC) in the Hague, which is looking into events since the Hamas terror attacks of October 7.
It said its War Crimes Team is "obliged to support any investigations opened by the ICC that could involve British subjects".
The posters say: "UK policing is supporting the work of the International Criminal Court, which is investigating alleged war crimes in Israel and Palestine from June 2014 onwards. Any evidence gathered may be shared with the ICC in support of their investigation.”
Mr Johnson described the new appeal as a “worrying politicisation of the Met Police”.
He told The Telegraph: “This sounds like a worrying politicisation of the Met Police - especially after Met officers were seen tearing down posters of Israeli hostages in Gaza.”
He went on: “When I was mayor I made it clear that we would not import foreign wars or disputes on to the streets of London. The Met would be better off fighting knife crime.”
Gideon Falter, the chief executive of the Campaign Against Antisemitism, said: “This poster campaign is utterly surreal.
“The first duty and priority of Britain’s police must surely be the safety and well-being of British people in Britain.
“The Met cannot hide its abject failure to discharge that duty over the past three months by turning attention to a foreign conflict.”
Scotland Yard said that its war crimes team had received more than 40 referrals “in recent weeks”, including from individuals returning from the region and any relevant information will be passed to the ICC.
A spokesperson for the Met police told the JC: “Under the terms of the 1998 Rome Statute, our War Crimes Team is obliged to support any investigations opened by the ICC that could involve British subjects.
"In order to meet our obligations to support the ongoing ICC investigation linked to Israel and Palestine, and due to the fact we were aware that relatively large numbers of people - including many British nationals - were returning on flights to the UK from the region, posters signposting how people could contact the War Crimes Team have been displayed at certain airports to make any potential witnesses or victims aware of how they can get in touch.”