German Chancellor Angela Merkel has warned that Turkey's EU bid will be in serious trouble if Ankara does not open its ports and airports to Cyprus.
Mrs Merkel's EU colleagues are deeply split over Turkey's bid
Mrs Merkel, whose government assumes the EU presidency in January, called on Turkey to "do all it can to prevent such a complicated situation arising".
She was speaking in an interview with Germany's Sueddeutsche Zeitung paper.
Turkey is demanding that the EU first end the economic isolation of Turkish-controlled northern Cyprus.
Mrs Merkel said Turkey "must know that there can be no simple 'business as usual' if there is no movement on the Ankara Protocol", which requires Turkey to have a customs union with Cyprus as well as the other new EU member states.
The draft of a European Commission report, due to be published on Wednesday, raises fresh doubts about Turkey's bid to join the EU.
COMMISSION'S DRAFT REPORT
Pace of Turkey's reforms has slowed
No progress towards normalising ties with Cyprus
Turkish military influence goes beyond defence
Freedom of expression below European norms
EU concerned about rights of women, Kurds and other minorities
The draft, seen by the BBC, says Ankara has made no progress towards normalising relations with Cyprus.
It also says the pace of reform in Turkey has slowed, and urges the Turkish government to guarantee greater freedom of expression and human rights.
The island has been divided since 1974, when Turkey invaded and occupied its northern third in response to an abortive Greek Cypriot coup backed by the former military government in Greece.
Turkish Prime Minister Recep Tayyip Erdogan has accused the EU of placing new obstacles on Turkey's path to EU accession.
"Don't ask us for things that aren't part of the programme," he said, adding that the EU should be "honest and sincere" in its approach.
The BBC's Oana Lungescu in Brussels says a partial freeze of talks may become inevitable by the end of the year, as Turkey shows no sign of keeping its promise over Cyprus.