Ivan Sirakov, Bulgaria’s ambassador to Austria, put the nation on a collision course with the EU as he said stopping the talks is “not in the EU’s interest” but Turkey “must be open and honest”.
Mr Sirakov used his speech in Vienna to assure Serbia, Montenegro, Bosnia-Herzegovina, Macedonia, Albania and Kosovo that “Europe would not be complete without them”.
He said: “The Western Balkans are very important for the security and wellbeing of Europe.”
Mr Sirakov added “we need Turkey for this process”.
Talks between the EU and Turkey are expected to pick up momentum this year following months of little progress amid the migrant crisis, attempted military coup and clashes over Ankara’s human rights record.
Farouk Kaymakci, Turkey’s permanent representative to the EU, said: “A summit between the EU and Turkey in June ahead of the EU summit is under consideration.
“There are expectations in this direction.”
The talks would come despite Turkey’s President Recep Erdogan restricting free speech by jailing respected journalists who have criticised him.
His policy extends to the internet with thousands of Twitter accounts and websites having been shut down by the government.
Mr Erdogan has also cracked down on the leaders and MPs of the pro-Kurdish opposition People’s Democratic Party (HDP).
The Turkish government has jailed elected HDP members of parliament.
Relations between Turkey and the bloc soured further last year, when German Chancellor Angela Merkel said she would encourage EU leaders to reconsider the accession talks if re-elected.
Mr Erdogan said in response: “What happened is Nazism. What happened is fascism.
“I’m not saying you are a Nazi, you are fascist. I am only defining what happened.”
EU leaders are expected to meet on June 28 – 29 and expanding the bloc will be one of the main items on the agenda.
Senior officials and ministers from candidate countries will be coming together in Bulgaria as it holds the bloc’s six-month rotating presidency.
Bulgaria’s foreign minister Ekaterina Zakharieva has expressed hope that relations between Turkey and the EU will improve.
She said: “Neither the successful protection of the EU’s external borders nor the fight against terrorism can be succeeded without a close partnership with Turkey.”
(Additional reporting by Monika Pallenberg.)