The White House said Monday said it is willing to take "additional steps" to defend US-allied fighters in Syria, warning the regime of Bashar al-Assad not to impede their actions.
Spokesman Josh Earnest said Syria "should not interfere" with operations by US-trained forces, warning that "additional steps" could be taken to defend them, raising the prospect of strikes against the regime.
Earnest said that Assad has not so far impeded the actions of US-backed groups, which include a 54-strong unit inserted into the Division 30 rebel unit in Aleppo province in mid-July.
Eight of them, including a commander, were kidnapped last week in a village in Aleppo province.
While the force has not come under attack from the regime it has been targeted by Al-Qaeda's Syrian affiliate the Al-Nusra Front, prompting US strikes.
The Pentagon has denied claims that US-trained members of Division 30 had been captured.
AFP contributed to this report.