US Secretary of State Rex Tillerson plans to remove Burma and Iraq from a US list of the world's worst child soldiers offenders, Us officials said, despite ongoing concerns from experts and diplomats.

The highly unusual intervention would break with longstanding protocol at the State Department over how to identify countries and foreign militaries which use child soldiers.

And it could prompt accusations the Trump administration is prioritising security and diplomatic interests ahead of human rights.

Three US officials with knowledge of internal deliberations at the department said Mr Tillerson overruled assessments on the use of child soldiers by his own staff and rejected recommendations by senior diplomats in Asia and the Middle East.

The Secretary of State also rejected an internal proposal from the State Department to add Afghanistan to the list, the sources said.

One official claimed the decisions have been made following pressures from the Pentagon to avoid complicating assistance to the Iraqi and Afghan militaries, which are close US allies in the fight against Isis.

Foreign militaries which appear on the list can face sanctions including a prohibition on receiving US military aid, training and US-made weapons unless the White House issues a waiver.

Human rights officials expressed surprise at the delisting, which was expected to be announced on Tuesday as part of the State Department's annual Trafficking in Persons report.

A State Department official said the report's content would not be disclosed until its release and the department "does not discuss details of internal deliberations".

The Pentagon did not immediately respond to a request for comment.

Under the Child Soldiers Prevention Act of 2008, the US government must be satisfied that "no children are recruited, conscripted or otherwise compelled to serve as child soldiers" in order for a country to be removed from the list.

But Child Soldiers International, a UK-based NGO which aims to stop the recruitment and exploitation of children by armed forces and groups, said Burma’s internal armed conflicts have been marked by severe human rights violations, with children widely used by both state armed forces and armed groups.

In a report in March 2016, the NGO found that four years after the UN and the Government of Burma signed a joint action plan to end the recruitment of child soldiers, “children continue to be present in the ranks of the Tatmadaw Kyi (state army) as well as non-state armed groups”.

Iraq, which has received more than $2bn (£1.6bn) in US arms and training over the last three years, was added to the State Department's "Child Soldier Prevention Act List" in 2016.

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Last year's State Department report said some militias of Iraq's Popular Mobilisation Forces (PMF) "recruited and used child soldiers". But, the flow of US assistance continued.

Ahead of the publication of the report, the State Department's Bureau of Democracy, Human Rights and Labour, which researches the issue, along with its legal office and diplomatic bureaus in Asia and the Middle East concluded the evidence showed both Burma and Iraq should be kept on the list.

Human Rights Watch said removing Burma from the list would be a "completely premature and disastrous action that will effectively betray more children to continued servitude and rights abuses”.

The decision also would put the Trump administration at odds with the UN, which continues to list the military in Burma, along with seven ethnic armed groups, on its list of entities using and recruiting child soldiers.

"What's particularly astonishing is this move ignores that the UN in Burma says that it is still receiving new cases of children being recruited" by the Burmese military, said Phil Robertson, deputy Asia director at Human Rights Watch.

Bordering both China and India, Burma is of growing strategic importance to the US at a time of increasing encroachment in the region by China, which is seeking closer relations with its neighbours.

Previously, former President Barack Obama handed out full or partial waivers regularly to Iraq, Burma, Nigeria and South Sudan.