By Laurence Norman in Brussels and Emre Peker in Istanbul 

The European Union and Turkey have negotiated an agreement on how to stem the flow of refugees into the bloc, European Council President Donald Tusk said on Sunday, as he urged EU leaders to back the deal at today's Brussels summit.

"After many weeks of hard work...we have reached an agreement which I hope will be accepted by all parties concerned," Mr. Tusk said, speaking before the meeting started in Brussels.

Sunday's meeting will "re-energize" often strained ties between the EU and Turkey, which Mr. Tusk called a "key partner" of the bloc.

German Chancellor Angela Merkel said the result of Turkey's EU membership negotiations remained "open," in comments ahead of the meeting.

At the heart of the proposed migration deal are Turkey's promises of tightening its border controls in exchange for some EUR3 billion ($3.19 billion) in cash and other benefits from the EU. Those include speeding up work on Turkey's EU membership bid and a new push to help Ankara win visa-free access to the bloc for its citizens.

"We need EUR3 billion," European Commission President Jean-Claude Juncker said on his way into the summit. Of that sum, the European Commission would come up with EUR500 million, and national EU governments should agree on how to come up with the rest at a later date, Mr. Juncker said.

However, underlining the continued lack of trust between Ankara and the EU, much of the focus ahead of Sunday's summit has been on how to guarantee the other side will keep to their pledges. Diplomats have noted the absence of Turkey's President Recep Tayyip Erdogan from Sunday's meeting.

EU officials also spent the weekend trying to persuade Cyprus to sign up for the deal. Cyprus has long blocked progress on Turkey's EU membership bid over Turkey's refusal to recognize the government in Nicosia.

The EU has been pressing Turkey to tighten controls on its boarders with Greece for some time. Formal talks started in September.

Migrants and refugees have crossed the sea from Turkey into Greece in their thousands in recent months, making Greece's eastern islands one of the main entry points for the biggest influx of migrants since the aftermath of World War II. Already this year more than 700,000 migrants, mainly Syrian, have arrived in the EU via Turkey, according to the International Organization of Migration.

Under the deal which has been negotiated, Turkey would toughen up its patrols in the Aegean Sea and on the land borders with Greece and Bulgaria, as well as cracking down on human-trafficking gangs. Ankara would agree to take back to Turkey migrants whose asylum claims are denied by EU countries.

The first EU-Turkey summit in 11 years comes as Ankara faces diplomatic and security challenges from Moscow following the downing of a Russian warplane on Tuesday.

While a joint response to the refugee crisis is top of the agenda, the Turkish delegation led by Prime Minister Ahmet Davutoglu is expected to press European counterparts on broader geopolitical issues led by the Syrian conflict, the fight against Islamic State, and Russia's increasingly assertive military operations in support of the Damascus regime just south of Turkey's border.

Before flying to Brussels for the summit, Mr. Davutoglu said Russia and Iran were propping up embattled Syrian President Bashar al-Assad under the guise of fighting Islamic State, warning that indiscriminate bombing campaigns were hitting civilians and threatening to unleash another wave of refugees.

"This matter is of direct interest to Turkey in the context of the refugee crisis, which is the main topic at the Turkey-EU summit," Mr. Davutoglu said.

Turkey would bring up Russia's repeated violations of the Turkish airspace with EU leaders. "This carries great importance with regards to creating a common stance in the Turkey- EU-Russia triangle," he said.

On Thursday, Turkey's EU Affairs Minister Volkan Bozkir said Ankara and the EU would start talks on a policy area covering economic and monetary policies as soon as Dec. 14-15. Turkey and the EU have started negotiations on 14 of the 35 policy criteria that Ankara must fulfill to join the bloc,

While the refugee crisis has strengthened Ankara's hand in negotiations, domestic developments in Turkey are complicating its efforts.

Two prominent Turkish journalists were jailed Thursday, pending trial, in connection with a report alleging Turkey has shipped weapons to Syrian rebels, which the government had repeatedly denied. Their arrests follow the government's seizure of opposition media outlets before elections in November. The U.S. and EU have both sharply criticized the moves.

Write to Laurence Norman at laurence.norman@wsj.com and Emre Peker at emre.peker@wsj.com

(END) Dow Jones Newswires

November 29, 2015 10:01 ET (15:01 GMT)