Turkey said it will hold a military exercise off northwest Cyprus for the next two weeks, amid growing tension with Greece over disputed claims to exploration rights in the east Mediterranean. The long-running dispute between Turkey and Greece, both Nato members, flared up after Ankara began exploring for gas off the coast of Cyprus. Both sides have held military exercises in the east Mediterranean, highlighting the potential for the dispute over the extent of their continental shelves to escalate into confrontation. Two weeks ago Greek and Turkish frigates shadowing Turkey's Oruc Reis oil and gas survey vessel collided, and Turkey's Defence Ministry said Turkish F-16 jets on Thursday prevented six Greek F-16s entering an area where Turkey was operating. On Friday night, Turkey issued a Navtex notice - an advisory message to mariners - saying it would be holding a "gunnery exercise" from Saturday until Sept. 11 off northwest Cyprus. The European Union's top diplomat said on Friday the bloc was preparing sanctions against Turkey that could be discussed at a summit in late September in response to Ankara's standoff with EU member Greece. EU diplomatic chief Josep Borrell said the bloc wanted to give "a serious chance to dialogue" but was steadfast in its support for member states Greece and Cyprus in the crisis, which has raised fears of a military standoff. A dispute over maritime borders and gas drilling rights has reignited the long-running rivalry between Athens and Ankara, with the two neighbours staging rival naval drills. EU foreign ministers meeting for talks in Berlin agreed to a request from Cyprus to sanction more individuals for their role in Turkey's exploratory drilling in waters claimed by the island. Mr Borrell urged Ankara to "abstain from unilateral actions" as a basic condition to allow dialogue - which Germany is trying to broker - to advance. "We agreed that in the absence of progress in engaging Turkey we could develop a list of further restrictive measures that could be discussed at the European Council on September 24 and 25," Mr Borrell said after the talks. Asked what these measures might entail, Mr Borrell said sanctions could be extended to ships or other assets involved in the drilling, as well as prohibiting the use of EU ports and supplies and restricting "economic and financial infrastructure related with this activity".