Turkey said it condemned this week's signing of a roadmap to boost two-way defence co-operation between the United States and the Republic of Cyprus.
The move came amid United Nations efforts to find common ground for the resumption of long-stalled negotiations between the rival Greek and Turkish Cypriot communities on the Mediterranean island, which has been divided for decades.
The US steps, including last June's announcement of the launch of a strategic dialogue with Cyprus, are detrimental to the security of the Turkish Cypriot side of the island, the Turkish foreign ministry said.
"These steps ... undermine the neutral USA position towards the island of Cyprus and make it more difficult to reach a just, lasting and sustainable settlement of the Cyprus issue," it said in a statement on Wednesday.
On Monday, the United States and the internationally recognised Republic of Cyprus signed the co-operation roadmap in Nicosia.
In a joint statement, their defence ministries reaffirmed their commitment to collaborate to tackle international security concerns via the roadmap.
Cyprus was partitioned in a Turkish invasion in 1974 after a brief Greek-inspired coup. Peace talks have been on hold since 2017.
The Turkish Cypriot side administers a breakaway state in the north of Cyprus recognised only by Ankara. It says a resumption of talks hinges on acceptance of its equal sovereignty with the Greek Cypriot government.
The Republic of Cyprus is one of four EU member states which is not a member of the North Atlantic Treaty Organization (NATO), and the only one not to participate in NATO's Partnership for Peace (PfP) program.
A former British colony, Cyprus hosts two UK military bases, Akrotiri and Dhekelia, officially the Sovereign Base Areas of Akrotiri and Dhekelia, a British Overseas Territory on the island of Cyprus, and a part of the United Kingdom.
(Edited by Georgi Gotev)