Only one percent of some 12,000 migrant children stuck in limbo in desperate conditions at refugee camps on Greek islands have had access to school, the UN said Monday.

"Out of 12,000 children on the islands, only one percent go to formal public school, said UN refugee agency (UNHCR) spokesman for Greece Boris Cheshirkov.

"Children are in despair, they need to be in a classroom and have a normality," Cheshirkov said, highlighting a plethora of problems including a lack of teachers and transport.

"Access to education is a big problem, especially on the islands," he added.

Cheshirkov noted that the registration and identification centers hosting the youngsters "were designed for a short time -- but the reality is different, they stay for many months." The children are dispersed across camps holding around 40,000 people in total on five islands in the Aegean Sea -- Lesbos, Chios, Samos, Leros and Kos.

Referring to a family that fled war-ravaged Syria, Cheshirkov said: "They left Syria four months ago when their house was destroyed, and their three kids have never gone to school because they were too young in Syria to go. Now that they are in Greece and at school age, their father Ibrahim, 49 years old, wants them to go to school (but) here they can't go."

Greece was overwhelmed by the migrant crisis which erupted in 2015 with tens of thousands of people arriving after making perilous crossings in barely seaworthy vessels via neighboring Turkey. Their stays in the camps have extended over long months, in squalid and unbearable conditions.

Last month, Doctors Without Borders (MSF) drew attention to the particular plight of minors and appealed to EU states to take urgent action to "put an end to this cycle of suffering", warning of the effect on the children's mental and physical health caused by conditions it termed inhumane.

The NGO has said it fears some children are left at increase suicide risks in dangerously overcrowded camps such as Moria on Lesbos.