Thousands of migrants detained in Greece for lacking the correct paperwork, including some asylum seekers and teenagers, have been held in often appalling conditions without access to basic hygiene and regular medical care, according to a medical aid ogranisation.

The report, released on Tuesday by Medecins Sans Frontieres, or Doctors Without Borders, said the detention policy causes "unnecessary suffering and harm", and that detainees were displaying increased mental health problems, incluidng suicide attempts and extreme forms of protest such a sewing up their mouthes.

Medecins Sans Frontieres expressed "grave concerns" and urged Greece to "put an end to the systematic and indiscriminate use of detention" for migrants found in the country without the correct documentation - many often picked up during random checks after living in Greece for years.

Respiratory and skin diseases abound, exacerbated by unsanitary, crowded conditions, the group said.

In one center, dozens of migrants are locked in cells without access to toilets for 22 hours a day, allowed out only for an hour in the morning and another in the evening, said Ioanna Kotsioni, who handles migration issues for MSF. If they need to use the bathroom during the day, they either have to attract the attention of a guard to allow them out of their cell, or use a plastic bottle.

Throughout the system, migrant detainees lacked access to basic items such as clothing, clean bedding and personal hygiene items such as soap, toothpaste and detergent, MSF said.

"The consequences on these people's health are very serious," Kotsioni said. "What we are asking is for this generalised, systematic detention to stop, as well as for an end to the detention of people in inappropriate facilities."

Greece is one of the main entry points for migrants trying to gain access into the European Union. Tens of thousands make the perilous journey each year, either attempting to cross over land from Turkey, or heading to Greek islands from the nearby Turkish coast, often in rickety boats that break down or sink.

In mid-2012, the Greek government launched a crackdown on illegal migration, nicknamed Operation Xenios Zeus, in which tens of thousands of migrants were rounded up from city streets for identity checks. Those found without residents permits or refugee papers were sent to detention centers pending deportation.

More than 6,000 people are held in migrant detention centers pending deportation, MSF said.

Hundreds, possibly thousands, more are held in police holding cells where conditions are even worse as detainees have no access to the outdoors, and often have no fresh air or natural light. Although the holding cells are not equipped to house people for more than two or three days at a time, Kotsioni said MSF has encountered migrants who have been held for up to 17 months.

Source: Agencies