Britain has expressed "regret" to Saudi Arabia after an egg was thrown at a Saudi military official during a visit to London, the Foreign Office said.
Anti-war activists last week attempted a citizen's arrest against General Ahmed Assiri, a spokesman for the Saudi-led Gulf coalition fighting rebels in Yemen, and then threw an egg that hit him in the back.
An FCO spokeswoman said Foreign Secretary Boris Johnson spoke to Saudi Deputy Crown Prince Mohammed bin Salman, son of the Saudi king and the country's defence minister, on Saturday.
"They discussed bilateral relations, regional issues and the humanitarian situation in Yemen," the spokeswoman said.
"The Foreign Secretary expressed his regret at the disturbance to Saudi Major General Assiri's visit to London on Thursday."
Saudi state media said that Britain had apologised.
Gen Assiri had said after the incident that he had been "subject to aggression" by protesters critical of Riyadh's operations in Yemen.
Footage on Twitter showed anti-war activist Sam Walton approaching Gen Assiri last week, putting his hand on the general's shoulder and announcing he was placing him under citizen's arrest, before being pushed aside by the official's security detail.
As the general, shielded by his bodyguards, entered a building, another protester threw the egg.
Video then showed Gen Assiri turning around and making a rude gesture towards the activist.
Human rights groups have criticised Saudi Arabia over its military action in Yemen, where thousands of civilians have been killed.
Riyadh began its campaign two years ago against Iran-backed Houthi rebels.
Amnesty International last month condemned Britain for transferring arms to Saudi Arabia, saying Yemeni civilians continued to "pay the price".
In recent weeks, Britain has strengthened ties with Gulf states including Qatar, which has announced plans to invest $5bn in the country in the coming three to five years.