The United Nations children's fund said Thursday that 14 million children are paying the price for warfare in Syria and neighbouring Iraq, with violence and hardship shaping their future.

"With the conflict in Syria now entering its fifth year, the situation of more than 5.6 million children inside the country remains the most desperate," UNICEF said in a statement.

The agency said up to two million children were living in areas of Syria largely cut off from humanitarian aid, and around 2.6 million children were out of school.

Almost two million Syrian children are living as refugees in Lebanon, Turkey, Jordan and other countries, "in addition to the 3.6 million children from vulnerable communities" in the host countries, UNICEF said.

"For the youngest children, this crisis is all they have ever known. For adolescents entering their formative years, violence and suffering have not only scarred their past; they are shaping their futures," said UNICEF chief Anthony Lake.

UNICEF said conflict in Iraq has also forced more than 2.8 million children from their homes.