Turkey announced on Friday that it would conduct gas exploration operations until September in a Mediterranean region, while Cypriot authorities said it was part of the exclusive economic zone of the island.
"We urge the Turkish authorities to stop these operations and we encourage all parties to exercise restraint," State Department spokeswoman Morgan Ortagos told Sky News.
EU Foreign Minister Federica Mugherini expressed "grave concern" over Turkey's announcement that it intends to conduct "gas exploration" activities in the exclusive economic zone of Cyprus.
"In March 2018, the European Council strongly condemned Turkey's continued illegal activities in the eastern Mediterranean," she said in a statement.
"In this context, we urgently call on Turkey to exercise restraint and respect for the sovereign rights of Cyprus in its exclusive economic zone and to refrain from any illegal action," she said, stressing that "the EU will respond to it in an appropriate form and in full solidarity with Cyprus."
In recent years, Cyprus, a member of the European Union, has signed gas exploration contracts with giant companies.