The president of the European Council, Donald Tusk, will present the EU position to Turkish Prime Minister Ahmet Davutoglu during the council's meeting of heads of state and government in Brussels, Belgium.
Tusk told reporters Thursday the talks will be difficult and intense, and he had three guiding principles: The agreement must be acceptable to all EU members; it must comply with international and EU law; and it must be part of a comprehensive strategy.
"I am cautiously optimistic, but frankly speaking, more cautious than optimistic," he said.
The plan was proposed earlier in the month, and the final wording is being discussed at this two-day meeting of the European Council.
European leaders are grappling with the biggest refugee crisis since World War II, with more than 1 million people having entered EU territory since the start of 2015.
The majority have come by using trafficking networks to cross the Aegean Sea, which separates Turkey and Greece, with more than 400 migrants dying in that crossing so far this year.
Most of the migrants are from Syria, where the civil war
has created more than 4 million refugees. More than 2.7 million refugees from Syria are in Turkey.
Turkey and the EU have been discussing a proposal to expedite Turkey's entry into the 28-member union
, to send refugees who left Turkey for Greece back to Turkey, and to provide Ankara with financial aid to deal with the influx.
Tusk spoke Wednesday of working toward "an agreement to further strengthen our cooperation with Turkey in order to stem the flow of migrants from Turkey to Europe."
'Not an issue of bargaining'
As he arrived at the EU summit, Turkey's Davutoglu told reporters the refugee crisis was not about bargaining.
"For us, for Turkey, the refugee issue is not an issue of bargaining but an issue of values -- humanitarian values as well as European values," the Prime Minister said.
"Of course, the EU and Turkey, we have the same goal, the same objective -- to help Syrian refugees especially -- and also to have a future in our continent, in a bright manner," he said.
German Chancellor Angela Merkel
, addressing her nation's legislature, also talked about "deepened cooperation" with Turkey and called Ankara's "demand for more financial help completely understandable."
At the same time, she said any discussions about migrants shouldn't take place in a vacuum. The other things happening in Turkey -- including criticisms of rights violations and its crackdown on Kurds -- matter, too.
"It ... goes without saying that we stress to Turkey, for example, the importance of freedom of the press (and) the freedom of the Kurds," Merkel said Wednesday. "As important as the necessary fight against the PKK's terror is, (Turkey must take a measured) approach ... for all Kurds."
The Kurdistan Workers' Party, also known as the PKK, is a Kurdish separatist group founded in the 1970s. It seeks and independent Kurdish state in Turkey.