The European Union began negotiations on Thursday on a new chapter of Turkey's EU membership bid - a condition of the bloc's migration deal with Ankara - but the two sides made no headway in a row over visa liberalization.
Turkey has officially been a candidate for EU membership since 1999, but progress has been slow, hampered by years of opposition from France and Germany, as well as geopolitical tensions over Cyprus.
Ankara demanded progress on its membership bid in exchange for its help in stemming migrant flows to Europe. The EU-Turkey migration agreement struck in March foresaw a new negotiating chapter being opened before July.
As part of the EU accession process, negotiations have to be conducted on 35 chapters, which each cover a policy area in which Ankara must meet EU standards.
The chapter opened Thursday covers financial and budgetary provisions: financial contributions to the EU's budget and Turkey's development of tools to "co-ordinate and ensure the correct calculation, collection, payment and control" of future contributions, according to an EU statement.
Sixteen chapters have now been opened, with negotiations concluded on one, relating to science and research. But the most sensitive topics - for instance justice, security and fundamental rights - have so far been avoided.
The prospect of closer ties between the EU and Turkey has proven controversial, amid concerns about Ankara's human rights record and the authoritarian behaviour of President Recep Tayyip Erdogan.
Under the EU-Turkey migration deal, Ankara was also offered the prospect of visa-free access to the EU for its citizens. However, Turkey must complete a series of predefined EU benchmarks before being granted this highly sought benefit.
The biggest sticking point is a demand for Turkey to restrict its definition of terrorism, amid concerns that Ankara has used an anti-terrorism law to crack down on the media and government opposition. Turkey has refused to budge on this requirement.
"We can only make amendments if we don't have to change the capacity of our fight against terrorism," Turkish Minister for European Affairs Omer Celik said ahead of talks in Brussels on Thursday.
On Tuesday, 43 people were killed in an attack on Istanbul airport. Turkish authorities have pointed the finger at the Islamic State extremist group.
The EU's intention "has never been to reduce Turkey's capacity to fight terrorism effectively," insisted European Commission spokesman Margaritis Schinas.
The aim is to bring Turkish laws in line with the EU and ensure proportionality, so that people such as journalists "who express in a non-violent manner their views ... do not find themselves being put in prison or charged," he added.
As part of the EU-Turkey deal, Brussels also pledged to provide an overall 3 billion euros to improve the lives of Syrian refugees in Turkey.
On Thursday, the European Commission proposed spending 1.4 billion euros of that on education, healthcare and social infrastructure projects within the next month. Member states must now consider the proposal.