At a 15-hour summit meeting in Brussels on Monday, the two sides agreed that Turkey would take back all Syrian refugees and economic migrants who reach Greece from Turkey, in return for billions of euros in aid, the right to visa-free travel to Europe for Turks within four months, and the revival of negotiations to give Turkey better access to the E.U.’s single market.

However, key details remained to be worked out and the 28 leaders ordered more work by officials with a view to reaching an ambitious package deal with Turkey at their next scheduled summit, on March 17-18.

The deal is the E.U.’s latest attempt to stop the flood of people coming to northern Europe (principally Germany and Sweden) through Turkey, Greece and the Balkan peninsula. Around 1.25 million people entered the E.U. that way last year fleeing war and poverty, and an increasing number of countries have resorted to border checks to stop the flow, threatening the freedom of movement across borders that has been one of the E.U.’s greatest achievements.

In a separate but related development at the summit, E.U. leaders also agreed to send more aid to Greece to enable it to process asylum applications properly, and stop ‘waving through’ refugees en route to Germany. E.U. Council President Donald Tusk said that “the irregular flow of migrants along the Western Balkan route has now come to an end.”

South-eastern Europe has witnessed some increasingly tense scenes in recent weeks, notably at the border between Greece and non-E.U. Macedonia, where Macedonian police have used tear gas to keep back crowds of migrants that Greece had dispatched northwards. Over 30,000 migrants are currently stranded in Greece due to border closures.

Greek Prime Minister Alexis Tsipras said the bloc must speed up the process of relocating asylum seekers from Greece to other E.U. countries as promised last September. E.U. states have so far taken in only a few hundred of a promised 160,000 people and central European countries have rejected the whole principle.

Turkish Prime Minister Ahmet Davutoglu told E.U. leaders that Ankara was willing to take back all migrants who enter Europe from Turkey in future, including Syrian refugees, as well as those intercepted in its territorial waters.

In exchange for stopping the influx, he demanded doubling E.U. funding through 2018 to help Syrian refugees stay in Turkey and a commitment to take in one Syrian refugee directly from Turkey for each one returned from Greece’s Aegean islands, according to a document seen by Reuters.

“With this game-changing position in fact our objective is to discourage illegal migration, to prevent human smugglers, to help people who want to come to Europe through encouraging legal migration in a disciplined and regular manner,” he told a news conference after the summit.

In addition to beefed-up resources for Greece, the heads of government also agreed that NATO warships would start patrolling the Aegean Sea between Turkey and Greece to enforce the deal. Britain, France, Germany and Canada are all deploying warships to the region to help the E.U.’s border service, Frontex.

One other notable element of the summit was a tacit agreement for the E.U. to mute its criticism of increasing political repression in Turkey. Three days ago, the Turkish government seized the best-selling opposition newspaper Zaman.

Tusk stressed in his comments that “freedom of speech and expression…are fundamental human rights, and added that “we cannot stay indifferent to the concerns raised in this context about what is now happening in Turkey.”

However, there was no suggestion that any of the E.U. leaders was willing to sacrifice the broader deal for the sake of Turkey’s opposition press.