The Pentagon is likely to announce in the coming days that there are about 2,000 U troops in Syria, two US officials said on Friday, as the military acknowledges that an accounting system for troops has under-reported the size of forces on the ground.

The US military had earlier publicly said it had around 500 troops in Syria, mostly supporting the Syrian Democratic Forces group of Kurdish and Arab militias fighting Islamic State in the north of the country.

Two US officials, speaking on the condition of anonymity, said the Pentagon could, as early as Monday, publicly announce that there are slightly more than 2,000 U.S. troops in Syria. They said there was always a possibility that last minute changes in schedules could delay an announcement.

That is not an increase in troop numbers, just a more accurate count, as the numbers often fluctuate.

An accounting system, known as the Force Management Level (FML), was introduced in Iraq and Syria during former President Barack Obama's administration as a way to exert control over the military.

But the numbers do not reflect the extent of the US commitment on the ground since commanders often found ways to work around the limits - sometimes bringing in forces temporarily or hiring more contractors.

Vladimir Putin meets Syrian president Bashar Assad

The force management levels are officially at 5,262 in Iraq and 503 in Syria, but officials have privately acknowledged in the past that the real number for each country is more than the reported figure.

The Pentagon said last December that it would increase the number of authorized troops in Syria to 500, but it is not clear how long the actual number has been at around 2,000.

Obama periodically raised FML limits to allow more troops in Iraq and Syria as the fight against Islamic State advanced.

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As that campaign winds down, it is unclear how many, if any, US troops will remain in Syria.

Most of them are special operations forces, working to train and advise local partner forces, including providing artillery support against Isis militants.

One of the officials said that the actual number in Iraq is not expected to be announced because of “host nation sensitivities,” referring to political sensitivities about US forces in Iraq.

In August, the Pentagon announced that there were 11,000 troops serving in Afghanistan, thousands more than it has previously stated.

US Defence Secretary Jim Mattis has in the past expressed frustration with the FML method of counting US troops in conflict zones.