Theresa May has held talks with Turkish president Recep Tayyip Erdogan which covered security co-operation and a £100 million-plus defence deal.
The Prime Minister and the controversial president discussed a range of issues including the political process in Cyprus, Bashar Assad's regime in Syria and the security situation in Somalia, Downing Street said.
Mrs May "underlined the importance of our strong security partnership" and expressed her desire to "deepen co-operation on a range of issues" during the phone call.
Downing Street would not say whether concerns about Mr Erdogan's human rights record were mentioned in the call.
A Number 10 spokesman said: "The Prime Minister and President Erdogan discussed the ongoing Cyprus settlement talks and the Prime Minister reiterated that while there remains an opportunity for an historic agreement to be reached, all parties need to be prepared to take bold steps.
"She added that the UK stands ready to play a role in seeking a solution.
"On Syria, the Prime Minister welcomed the progress made at the Astana talks and praised Turkey's constructive role in helping to establish de-escalation zones.
"She underlined the importance of the talks being linked to a broader political process, culminating in a transition of power away from Assad."
The two leader "reaffirmed their desire to explore the opportunities presented by Brexit" on trading relations.
"They noted the progress made towards the signature of a deal between Turkish Aerospace Industries and BAE Systems for the preliminary design phase of the Turkish Fighter, and agreed this was a sign of the deepening defence industry relationship between Turkey and the UK.
"The two leaders looked forward to the upcoming Somalia Conference and the Prime Minister welcomed the substantial contribution Turkey has made, as well as their strong leadership in improving security in Somalia.
"The Prime Minister and President Erdogan concluded by looking forward to meeting at the Nato Summit in Brussels later this month."