Donald Tusk said after meeting with Greek Cypriot leader Dimitris Christofias in Nicosia that any attempt to weaken Greek Cyprus' EU presidency would be perceived as a bid to weaken the bloc itself.
Cyprus was split in 1974 when Turkey intervened after a coup by supporters of union with Greece. Ongoing, UN-facilitated talks to reunify the island's Turkish Cyprus and internationally recognized Greek Cyprus have made little tangible progress since they began in 2008.
Greek Cyprus joined the EU in 2004, but only the south enjoys membership benefits.
Turkey, an EU membership candidate, doesn't recognize Greek Cyprus as a sovereign country and has threatened to freeze its relations with the bloc if the island takes over the presidency before a reunification accord is reached.
Turkish Cypriot President Derviş Eroğlu has said that there would be no point in carrying on with talks after June, but Christofias insists that negotiations ought to continue even during the Greek Cypriot EU presidency.