The EU announced Thursday that it has allocated to Turkey the full six billion euros Ankara sought in return for its hosting of Syrian refugees.

After the biggest refugee crisis since World War II in 2015 saw a million people arrive in Europe, Brussels and Ankara agreed in 2016 to resolve the issue.

Under the deal, Turkey pledged to accept the return of migrants arriving in Greece and do more to stop the flow in exchange for six billion euros ($7.20 billion).

President Recep Tayyip Erdogan has accused the EU of not fulfilling promises and says Ankara has spent $40 billion on more than 3.6 million Syrian refugees living in Turkey.

"Today marks the finalisation of the contracting of six billion euros in EU support to refugees and host communities in Turkey," said Nikolaus Meyer-Landrut, the bloc's envoy to Ankara.

The two sides have "put an important milestone behind us and (will) now focus on making sure that the refugees and host communities will benefit from our projects."

The EU money has been earmarked for specific social projects inside Turkey for helping refugees and will not be paid directly to the Turkish government.

The issue has put a significant strain on relations between the bloc and Turkey.

Earlier this year, Erdogan said Turkey would not prevent migrants from leaving for EU territory but later rescinded the threat.

He sought to pressure Brussels into providing more support to Turkey in view of the Syrian conflict, especially after violence flared in the northwestern region of Idlib.

The new contracts include supporting health services for migrants and improving the living conditions of the most vulnerable refugees.

They have fled to Turkey since the conflict broke out after anti-government protests in Syria in 2011, with a death toll of nearly 400,000.

Tensions between the bloc and Turkey are high over Ankara's energy exploration in the eastern Mediterranean Sea in waters claimed by Greece.

The bloc said after a European Council summit last week that it plans more sanctions against Turkey.

But it added that the EU was "prepared to continue providing financial assistance to Syrian refugees and host communities in Turkey".