Greece deported a second batch of more than a hundred migrants to Turkey on Friday under a controversial deal to stem mass migration as Germany announced a sharp drop in asylum claims.

Police sources said a first boat left the Greek island of Lesbos carrying 45 Pakistani men, while a second carried 79 migrants, also mainly Pakistanis, back across the Aegean Sea where hundreds have lost their lives in a quest to reach Europe.

A small group of activists leapt into the water, clutching onto the anchor of the first ferry in an unsuccessful bid to stop a deportation effort which rights groups have harshly criticised.

Some 30 protesters also gathered at Lesbos' port, chanting "Stop deportations", "EU, shame on you" and "Freedom for the refugees".

Hours later the boats arrived in the Turkish harbour town of Dikili where the downcast migrants, clutching blankets and with small backpacks on their shoulders, were escorted off the vessels by security officials.

Meanwhile, several European foreign ministers were heading on Friday to Greece and Turkey to discuss the latest developments in the migrant crisis, Dutch officials said.

The deportations are taking place under a deal between Turkey and the European Union, which is straining under the pressure from the unprecedented flow of migrants into its territory.

Turkey is a main launching pad for the migrants fleeing war and poverty in North Africa and the Middle East - many of whom are from Syria - for a better life in Europe.

Turkey has promised to take back all irregular migrants landing on the Greek islands since March 20 - a figure which currently stands at about 6,000 - while Europe has agreed to resettle one Syrian refugee directly from camps in Turkey for each Syrian deported.

The threat of deportation is aimed at discouraging people from making the often deadly crossing in flimsy boats.

The transfers began on Monday with some 200 migrants returned to Turkey, but then stalled after a last-minute flurry of asylum applications by those desperate to avoid expulsion.

Human rights watchdogs say the scheme is badly flawed, and have raised concerns that migrants may not have the chance to apply for asylum before being deported.

'Off to good start'  

While concerns remain over the deal, Germany - Europe's top destination for refugees - said it had "got off to a good start".

Interior Minister Thomas de Maiziere announced that asylum applications had dropped 66% in March.

"In December 2015, it was 120,000 people, in January 90,000, in February 60,000 and in March 20,000," he said.

De Maiziere has warned that the shutdown of the Turkey-Greece route may encourage more migrants to attempt the even more dangerous Mediterranean crossing from Libya to Italy.

German Chancellor Angela Merkel, whose country took in 1.1mn asylum seekers last year, said on Thursday she was "very happy" with the way the migrant crisis was being tackled.

The drop in migrant numbers appears largely due to much-criticised border closures in the Balkans, as well as an increased clampdown by Turkey on people smugglers.

Turkish state media said this week that 400 smuggling suspects had been arrested so far in 2016, and more than 65,000 migrants intercepted at sea and on land.

Nothing for nothing  

While Europe appears to be getting its side of the bargain, Turkey warned the EU on Thursday against breaking the promises it made in return.

"There are precise conditions. If the European Union does not take the necessary steps, then Turkey will not implement the agreement," Turkey's President Recip Tayyip Erdogan said.

Turkey is slated to receive benefits including visa-free travel for its citizens to Europe, promised "at the latest" by June 2016.

Migrants and refugees argue with Greek policeman after they tried to open the border fence at a makeshift camp at the Greek-Macedonian border near the village of Idomeni.

Turkey is also to receive a total of €6bn ($6.8bn) in financial aid up to the end of 2018 for the 2.7mn Syrian refugees it is hosting.

Turkey's long-stalled accession process to join the EU is also supposed to be re-energised under the accord.

Rights groups have criticised these concessions as a "dirty deal", with the EU accused of turning a blind eye to Erdogan's slide into authoritarianism and crackdown on press freedom.

Amnesty International has said Turkey could not be considered a "safe country" for the return of refugees.

Erdogan argued Turkey deserved something in return for its commitment to Syrian refugees, on whom it has spent some $10bn since the Syrian conflict began in 2011.

"We have received lots of thanks for our action on the refugees and in the fight against terrorism. But we are not doing this for thanks ... Everything should happen in line with what has been promised, what has been set out in the text."