Britain has apologised after an egg was thrown at a Saudi military official during a visit to London, Saudi state media said Sunday.
An anti-war activist last week attempted a citizen's arrest of General Ahmed Assiri, spokesman for the Saudi-led Gulf coalition fighting rebels in Yemen, before another threw an egg that hit Assiri in the back.
British Foreign Secretary Boris Johnson called Deputy Crown Prince Mohammed bin Salman, son of the Saudi king and the country's defence minister, to apologise for "the attack on General Ahmed Assiri, counsellor to the prince, by protestors," the state-run SPA news agency said.
Assiri told AFP he had been "subject to aggression" by protestors critical of Riyadh's operations in Yemen.
Video posted on Twitter showed anti-war activist Sam Walton approaching Assiri, putting his hand on the general's shoulder and announcing he was placing him under citizen's arrest before being pushed aside by security personnel.
Walton can be heard saying, "I'm placing you under citizen's arrest for war crimes in Yemen."
Civilians in Britain are permitted to arrest anyone suspected of committing an indictable offence.
Another protestor followed Assiri's security detail to the entrance of a building, where he threw an egg that hit the general in the back. Video showed Assiri turning around and giving the protestor the finger.
Rights groups have harshly criticised Saudi Arabia over its military action in Yemen, where thousands of civilians have been killed in the two years since Riyadh intervened against Iran-backed Huthi rebels.
Amnesty International last month condemned Britain for transferring arms to Saudi Arabia, saying Yemeni civilians continued to "pay the price".
The London-based rights group described the transfers as a "shameful contradiction" of British aid efforts in Yemen.
Britain has in recent weeks moved to strengthen ties with Gulf states including Qatar, which last week announced plans to invest $5 billion in the United Kingdom in the coming three to five years.
Prime Minister Theresa May also attended a Gulf Arab summit in December for talks on trade.