The United States on Tuesday demanded that Turkey pull back an energy research ship that it has sent back to waters contested with Greece, calling the move a "calculated provocation."
In a strongly worded statement, the State Department said the US "deplores" the decision by Turkey that came just after tensions with Greece had subsided.
"We urge Turkey to end this calculated provocation and immediately begin exploratory talks with Greece," State Department spokeswoman Morgan Ortagus said in a statement.
"Turkey's announcement unilaterally raises tensions in the region and deliberately complicates the resumption of crucial exploratory talks between our NATO allies Greece and Turkey," she said.
"Coercion, threats, intimidation and military activity will not resolve tensions in the Eastern Mediterranean."
Turkey in August sent an exploratory ship into contested waters backed by warships, alarming both Cyprus and Greece, which carried out military drills.
Tensions subsided after Turkey withdrew the ship and agreed to exploratory talks with Greece.
But the Turkish navy said the Oruc Reis ship will restart activities in the region, angering Greece which said there can be no talks until it is withdrawn.
Secretary of State Mike Pompeo late last month visited Greece in a show of support and hailed lowering tensions.