UPDATE: 6:37 a.m. EDT — A senior Turkish official said Thursday that Turkey will not make new demands at a meeting with EU leaders in Brussels as officials meet to finalize a deal.

“It will be hard to get a result from this summit, but not impossible. The reason is there are too many actors on the EU side,” the official told Reuters. “Some countries should not be allowed to exhibit a manner that would block progress.”

Original story:

As EU leaders prepare to meet to finalize a deal with Turkey over the influx of refugees, European Council President Donald Tusk said a "catalogue of issues" in the way of an agreement still remain unresolved. Tusk’s comments come a day before Turkish Prime Minister Ahmet Davutoğlu is due to join a summit Friday.

Last week, European leaders agreed on the outlines of a “one in, one out” deal with Turkey that will, for every Syrian refugee resettled in Europe, see one Syrian refugee returned to Turkey from the Greek islands. German Chancellor Angela Merkel backed the proposed agreement, calling it a “breakthrough” that would deter refugees from making the perilous sea crossing.

"Work is progressing, but there is still a lot to do," Tusk wrote to leaders, inviting them to the summit he will chair, according to Reuters.

In the meeting last week, where the plan was initially proposed, EU leaders also reportedly said that in return for Turkey’s action to help ease the refugee crisis, visa-free travel to Europe for Turkish citizens would be made available from June.

However, visa-free travel to the Schengen area for Turkish citizens will reportedly depend on Turkey complying with all 72 conditions that the EU has set out, BBC reported. As part of the agreement, Turkey is also expected to receive an extended aid package of 6 billion euros ($6.7 billion) in exchange for taking back and, in some cases, repatriating migrants.

Meanwhile, Spain’s foreign minister said his country would oppose the "blanket return" of refugees to Turkey.

Amid increasing debate over the EU-Turkey deal, head of the European Commission, Jean-Claude Juncker reportedly said ahead of the Friday summit that he was "cautiously optimistic" a deal could be reached.

The deal, which was presented in a draft by Tusk for approval, makes clear that the total number of refugees to be settled in EU is likely to be limited to about 72,000 out of nearly 3 million Syrians in Turkey.

The draft, which was seen by Reuters, also said that the plan is "to break the business model of the smugglers and to offer migrants an alternative to putting their lives at risk," adding that the aim is to bring "a temporary and extraordinary measure which is necessary to end the human suffering and restore public order."

Hundreds of thousands of migrants have travelled through Macedonia over the past year after making the dangerous sea crossing from Turkey, with the aim of entering Europe. Over 13,000 refugees fleeing their homelands in the Middle East are stuck in unhygienic camps in Greece, most with few options of anywhere to go, since Macedonia has severely limited the entry of refugees.

Apostolos Tzitzikostas, governor of Greece's central Macedonia prefecture, said earlier this month: "We can no longer shoulder this strain by ourselves," Agence France-Presse reported.