The Queen had held a private audience with Turkish president Recep Tayyip Erdogan at Buckingham Palace.
The head of state greeted the controversial Turkish leader in the 1844 Room of her central London residence.
Protesters have been demonstrating ahead of Mr Erdogan’s talks with Prime Minister Theresa May on Tuesday afternoon.
Critics accused the PM of “cosying up” to the totalitarian leader for economic reasons as she prepared to host him in No 10.
Mr Erdogan, who is on a three-day visit, has faced condemnation for purging his opponents, continuing decades of Turkish opposition to Kurdish autonomy and targeting Kurds fighting Islamic State in Syria.
.@theresa_may will be meeting with Turkish President #ErdoÄan today. Will she call for the release of #Turkey's dozens of jailed journalists, or turn a blind eye in favour of trade deals? Read @RSF_inter's letter. https://t.co/uRvxvgwB2D #FreeTurkeyMedia #pressfreedom pic.twitter.com/6yUhIHpN6D— Rebecca Vincent (@rebecca_vincent) May 15, 2018
Protest groups gathered outside Downing Street, including organisations supporting journalists, such as Reporters Without Borders, the Cartoonists Rights Network International and the Index on Censorship.
Many protests outside Downing Street this morning ahead of #Erdoganâs visit. We call on @Theresa_May to raise the issue of #Turkeyâs 155 imprisoned journalists. #FreeTurkeyMedia #JournalismIsNotACrime pic.twitter.com/9VR9zAvreW— Index on Censorship (@IndexCensorship) May 15, 2018
Around 250 journalists and media workers are in jail in Turkey.