The Burmese army has released 109 children from its military ranks in its single biggest discharge of child soldiers, but boys are still being illegally recruited from poor families, the United Nations said.

Burma has for years been listed among countries where children have been recruited to fight - both by government forces and rebels.

Bertrand Bainvel, head of the UN children’s fund in Burma, said the military wants to professionalise its ranks and the presence of child soldiers may block military cooperation with other countries.

A reformist, semi-civilian government that took over in 2011 has been working with the United Nations to get children out of the military. It has released 472 children since June 2012, including Thursday’s discharge, which was the largest yet, according to the UN.

“There is a commitment by the Tatmadaw to have this practice eradicated from its ranks,” said Bainvel, referring to the military by its traditional name.

Bainvel said recruitment continues at a decreased rate and that most young recruits come from poor families seeking the income that a son in the army can provide.

Recruiting most often takes place in the two largest cities, Rangoon and Mandalay, and is often done through civilian brokers who forge identification documents, making it difficult to determine how many child soldiers remain enlisted.

“This is a big question and there’s no way to say for sure how many there are,” Bainvel said.

The UN said seven ethnic minority guerrilla forces, which have fought or are still fighting the government, were also using child soldiers.