ATHENS (AFP) - Six migrants who were fed up with being stuck on the Greek Island of Chios tried to make their way back to Turkey - by swimming, Greek harbour police said on Wednesday (May 11).

Two groups of swimmers were picked up on Monday and Tuesday, several hundred metres off the coast of Chios, the police said. The Turkish coastline, just nine nautical miles away, is visible from the island.

Like hundreds of thousands of people before them, they had reached Chios by crossing the same stretch of water on makeshift boats, often overloaded with desperate people.

The first group included four Iraqis who tried to swim back by clinging onto a rubber ring. It was not immediately clear who was in the second group.

Under terms of a controversial March 20 agreement between Brussels and Ankara aimed at easing the migrant crisis, all "irregular migrants" arriving on the Greek islands face the prospect of being deported to Turkey. The aim is to discourage people from making the perilous Aegean crossing.

According to the Ethnos daily, they were among those slated for deportation and had hoped that by making their own way back, they could arrive incognito, thereby avoiding detention by the Turkish authorities on their return.

So far, more than 300 people have been sent back, with rights groups saying their fate was unclear.

There are currently 8,400 migrants on the Greek islands, officials said Wednesday, most of whom are waiting for their asylum applications to be processed.

New arrivals are confined to camps for 25 days, after which they are allowed out but cannot leave the islands.

Separately there are another 45,000 migrants and refugees who arrived in Greece before the March 20 deadline who have been stuck since the Balkans state began closing their borders in mid-February.