EU leaders have agreed a joint position to put to Turkey in an attempt to reach a deal over the migrant crisis, Luxembourg's prime minster says.

Xavier Bettel said the common EU position would be put to Turkish PM Ahmet Davutoglu on Friday morning.

The proposed deal would see all migrants travelling to Greece from Turkey sent back.

In return it is thought the EU might offer Turkey financial aid and visa-free access to Schengen countries.

German Chancellor Angela Merkel said that Turkey had to meet international standards of protection for all migrants, Reuters reports.

She said that legal resettlement of Syrian refugees from Turkey to the EU under the deal could start a few days after the first returns from Greece.

However, she added that the EU needed to be ready to start returning migrants from Greece to Turkey rapidly to avoid a "pull factor" creating a surge of migrants before the new system takes effect.

Lithuanian President Dalia Grybauskaite has warned that the plan to return people to Turkey is "on the edge of international law" and difficult to implement.

Mr Davutoglu has said he will not accept Turkey becoming an "open prison" for migrants.

To meet concerns over the plan's legality, the leaders discussed providing assurances that each person claiming asylum will be given a full hearing in Greece, the BBC's Damian Grammaticas reports from Brussels.

French President Francois Hollande warned that "I cannot guarantee that there will be a happy outcome" to the search for a solution.

Since January 2015, a million migrants and refugees have entered the EU by boat from Turkey to Greece. More than 132,000 have arrived this year alone.

Tens of thousands are now stuck in Greece as their route north has been blocked.

Under initial proposals, for each Syrian migrant returned to Turkey, a different Syrian would be resettled in the EU directly from the country.

In return, the EU had suggested it would double financial aid to Turkey promised last year, make a fresh push on talks over Turkey's eventual membership of the EU and offer visa-free travel to Europe's Schengen states.

However, those proposals have since been watered down, lowering expectation on greater financial help and talks on EU membership and linking visa-free travel to 72 conditions to which Turkey must agree.

A number of EU countries have raised concerns about what is on offer to Turkey amid a clampdown by the Ankara government on academics and journalists.