The EU and Turkey have ended a summit in Brussels and delayed a decision on how to ease the migration crisis.
Leaders have been discussing an offer by Turkey to do more to stop illegal migration in return for more EU aid and accelerated EU membership talks for Turkey.
They said they had agreed on the broad principles of a plan but needed more time to work on the details of a deal.
Talks will continue ahead of a long-scheduled EU meeting on 17-18 March.
Europe is facing its biggest refugee crisis since World War Two, with most migrants coming via Turkey.
Turkey is currently sheltering more than 2.7 million refugees from the civil war in neighbouring Syria. The EU wants Turkey to take back migrants who do not qualify for asylum and do more to patrol its own waters.
For every migrant sent back, Turkey wants the EU to accept one Syrian refugee from Turkish soil through a resettlement scheme.
The Turkish government is asking for a doubling of EU aid aimed at helping Turkey deal with the crisis, to €6bn ($6.6bn; £4.64bn) as well as a faster path towards EU membership and the speeding up of plans to allow Turks visa-free travel in Europe.