BRUSSELS—The European Union's deal with Turkey to prevent large flows of migrants entering the bloc continues to work, but Greece still has to do more to improve reception facilities for asylum seekers, the EU's executive arm said Wednesday.

In a set of reports on the bloc's migration policy, the European Commission said that the "sharp and continued decrease of people crossing irregularly or losing their lives in the Aegean" proves that the deal, struck in March between the EU and Turkey, is working.

On average, some 85 people arrived every day since June, in comparison to over 1,700 a day in the month before the deal and 7,000 a day in October 2015.

"Over the past 12 months, we have come a long way," said migration commissioner Dimitris Avramopoulos. But he added: "The refugee crisis is not over; that's why the progress made so far has to be sustainable."

However, part of the deal—under which one Syrian refugee would be resettled from Turkey into Europe in return for every Syrian who crossed illegally from Turkey to Greece and was sent back—seems to have made little progress. Only 576 migrants had been sent back from Greece to Turkey, mostly non-Syrians, while 1,614 Syrian refugees had been resettled from Turkey to EU countries since March.

Mr. Avramopoulos said that while Greece has "significantly increased its reception capacity" for refugees and adjusted laws to allow for legal aid and education of asylum seekers, " much more needs to be done" for the country to have a functional asylum system and to allow other EU countries to send asylum seekers back to Greece. Under EU rules, migrants must file for asylum and stay in the first country of arrival or be returned there from other EU countries.

But given the poor conditions for asylum seekers in Greece who sued in EU courts, EU countries in recent years have refrained from sending asylum seekers back to Greece. Mr. Avramopoulos said that the goal remains to improve conditions for a "gradual resumption" of migrant transfers to Greece but that "we need to avoid that an unsustainable burden be put on Greece."

He called on countries to step up a parallel program of redistributing a total of 160,000 asylum seekers from Italy and Greece more evenly across the bloc. So far, only 5,651 migrants have been taken by other countries under that program.

In response to claims by Turkish President Recep Tayyip Erdogan, who regularly says the EU hasn't paid a cent of the €3 billion ($3.4 billion) it promised as part of the migration deal, the commission said a total of €2.2 billion has been allocated for refugees in Turkey, out of which €1.2 billion has been contracted and €467 million already paid.

The commission said it was continuing to work with the Turkish government to make the legislative changes needed for the EU to grant Turkish citizens visa-free travel to the bloc. The Council of Europe, the continent's intergovernmental human rights body, is involved in negotiations with Ankara on adjusting the country's antiterror laws so as to limit the prosecution of dissidents on terrorism charges.

The European Parliament and several EU governments have indicated that they won't approve visa-free travel unless the use of the antiterror law is limited in scope, a change Mr. Erdogan has repeatedly refused to approve, citing security concerns related to the Kurdish insurgency and the recent failed coup attempt.

Countries that introduced border checks within the border-free Schengen area in response to last year's migration crisis can keep those checks in place, the commission said. "The controls have been proportionate and justified," Mr. Avramopoulos said, adding that in November, a decision will be made on whether border checks put in place by Germany, Austria, Denmark, Sweden and Norway should be extended by another six months.

Write to Valentina Pop at valentina.pop@wsj.com

(END) Dow Jones Newswires

September 28, 2016 09:15 ET (13:15 GMT)