The US military has moved additional troops into Syria in recent days to help provide protection to other American service members as they withdraw under President Donald Trumps directive to pullout all his country’s troops from there, two US defense officials told CNN. The officials would not reveal where in the country the troops are or how many have been sent, it said. Defense officials have acknowledged that a security force of armed troops -- possibly infantry -- would be needed to help carry out the withdrawal of US forces over time, said the report. The Pentagon officials said the additional security forces may move around Syria to different locations as needed and may move in and out of the country at times. They would not indicate if any troop withdrawals have taken place or will happen in the immediate future, citing security concerns. The news comes after ISIS claimed responsibility for a deadly explosion that killed four Americans and at least 10 other people in the Syrian city of Manbij last week. Trump’s decision to withdraw from the war-torn country has left Kurdish and Arab fighters known as the Syrian Democratic Forces, or SDF, exposed. The SDF has been among the most effective forces in the battle with ISIS but is under threat as Turkey threatens a new offensive in Syria.