Theresa May will visit Turkey on Saturday for talks with President Recep Tayyip Erdogan, Downing Street has said.
The prime minister is expected to discuss trade, defence and security.
Mrs May is likely to fly to Ankara from the US, where she is meeting President Trump on Friday, Number 10 said.
It will be Mrs May's first visit to Turkey as PM and comes in the wake of Mr Erdogan's clampdown on opponents after the failed coup in July 2016.
Asked whether Mrs May will raise concerns over the clampdown during her talks with Mr Erdogan and Prime Minister Binali Yildirim, a Number 10 spokesman said: "We have been clear in our support for Turkey's democracy and institutions since the coup last summer.
"The PM will take this opportunity to reiterate our support for that, but we've also been clear that Turkey's response to that must be proportionate and of course we will continue to raise those issues.
"The visit will reflect the fact that Turkey is an indispensable partner and a close ally for the UK on many issues of global importance, including trade, security and defence."
It also comes after 39 people were killed in an attack on a New Year's Eve party in a nightclub in Istanbul.
So-called Islamic State it was behind the attack and the militant group was linked to at least two other attacks in Turkey last year.