KABUL, Afghanistan — Alarmed that large stretches of Helmand Province are falling to the Taliban, American Special Operations forces have secretly taken a more central role in the fighting to save crucial areas of the province, as more air power and ground troops have been committed to the battle, according to Western and Afghan officials.

A Western diplomat said last week that United States Special Operations forces had been engaged in combat in Helmand for weeks, and that there were more American forces fighting there than at any time since President Obama last year announced a formal end to combat operations in Afghanistan.

The extent of the American role has been kept largely secret, with senior Afghan officials in the area saying they are under orders not to divulge the level of cooperation, especially by Special Operations forces on the ground. The secrecy reflects the Pentagon’s concern that the involvement may suggest that the American combat role, which was supposed to have ended in December 2014, is still far beyond the official “train, advise and assist” mission.

The elite ground units in Helmand include both Special Operations troops and the United States Air Force’s Special Tactics Squadron, according to the Western diplomat, who spoke on the condition of anonymity to avoid angering his colleagues.