A small number of US special operations forces will be sent to northern Syria to work with local troops in the fight against Islamic State militants, the White House has announced.
The deployment marks the first time Americans will have been deployed openly on the ground in the country.
President Barack Obama ordered the deployment of fewer than 50 commandos to help coalition forces co-ordinate with local troops, White House spokesman Josh Earnest said.
He insisted their role should not be described as a “combat mission”, saying the troops would train, advise and assist local forces in an intensification of the US effort against IS.
He acknowledged the forces would be taking risks in a dangerous part of the world, where the US also is conducting air strikes.
“There’s no denying the serious risk they will be facing,” Mr Earnest said, but “they are not in a combat mission”.
Officials would not say exactly how many troops would go to Syria, detail their role or say how long they would stay.
US troops have been on the ground in Syria before, Mr Earnest said, noting a rescue mission more than a year ago and a more recent raid.
Although the number is small, it marks an escalation of US involvement in the fight against IS, which controls a large part of northern Syria and has its self-proclaimed capital in the city of Raqqah.
The move comes after weeks of deliberation on how to revive the struggling effort in Syria and the failed training and equipping mission there, and follows a visit to the region last week by Marine General Joseph Dunford, the new chairman of the Joint Chiefs of Staff.
One senior official said that a first group of forces – possibly a couple of dozen – will go relatively soon to assess the situation and determine which groups on the ground the US can best work with, including moderate Kurdish and Arab fighters.
More special operations forces will follow once the US determines what the needs are. The initial forces to move in are likely to come from within the region, and they may be supplemented later with commandos from outside the area.
Defense secretary Ash Carter hinted at the possible changes earlier this week, saying Washington was retooling its strategy in Iraq and Syria and would conduct unilateral ground raids if needed to target IS militants.
The US has carried out special operations raids in Syria, and it participated in a ground operation to rescue hostages last week in northern Iraq that resulted in the first US combat death in that country since 2011.
The addition of special operations forces marks a shift for Mr Obama who has steadfastly said he would not put US boots on the ground in Syria.
In recent weeks, US military officials have been signalling greater acceptance for the idea of such a deployment.
Mr Carter told the Senate Armed Services Committee that the US would do more to support moderate Syrian forces fighting IS.
Last week, Gen Dunford met his top commanders during a stop in Iraq, and told them to broaden their thinking and map out new ways the US-led coalition could put more pressure on IS fighters.
The US will also be sending additional aircraft, including F-15 fighters and A-10s, to Incirlik air base in Turkey, repositioning them from other spots in the region.