BRUSSELS - The European Union (EU) clinched an agreement with Turkey on late Sunday, offering 3 billion euros(3.18 billion U.S. dollars) in aid and more promising access for Ankara's membership to the bloc, to trade for massive reduction of illegal migrant arrivals.

European Council President Donald Tusk made the announcement at a press conference after Sunday's summit, which was attended by leaders of the 28-country bloc and visiting Turkish Prime Minister Ahmet Davutoglu.

Brussels has been negotiating with Ankara since September on strengthening the country's border controls with Greece in a bid to stem the unexpected migrant or refugee influx as the continent is experiencing the most severe migrant crisis since the aftermath of the Second World War.

Some 1.5 million illegal migrants have arrived the EU so far this year, according to Tusk. He vowed a joint effort from Turkey, where some 2.2 million Syrian refugees are living, to stem the irregular refugee flows.

Turkey's neighboring country Greece has since been a gateway for 700,000 more asylum seekers, also mainly from war-torn Syria, according to International Organization for Migration.

Under the agreement, the EU will offer 3-billion-euro aid to Ankara to help improve the living conditions of millions of asylum seekers in Turkey.

Davutoglu said in the press conference that his country has spent 8 billion dollars to deal with the refugees, stressing that Europe's 3-billion euro humanitarian aid "is given to Syrian refugees, not given to Turkey."

The EU also agreed to speed up work on Ankara's membership bid to the 28-nation bloc and Turkish visa-free access to the EU.

Turkey has been a candidate to the EU since 1999 and negotiating for accession since 2005. The two sides Sunday agreed that "the accession process needs to be re-energized."

According to their joint statement published by the EU, the EU and Turkey will "adopt result-oriented action to prepare their common future...to confront and surmount the existing risks and threats in a concerted manner to reinforce the European Project."

Turkey will also further work on its visa liberalization roadmap and get assessment from the EU step by step. The lifting of visa requirements for Turkish citizens in the Schengen zone is expected to complete by October 2016.

The two sides decided to hold regular summits twice a year to "assess the development of Turkey-EU relations and discuss international issues."