In new comments, Joint Chiefs of Staff Chairman Gen. Joe Dunford said the US is planning "decisive military action" against ISIS targets inside Libya, and that while the decision hasn't been finalized, it will be in the next few weeks.

Other officials say that US special forces have been engaged in "clandestine reconnaissance missions" in Libya for months, aiming to map out the networks of ISIS in the country ahead of the attack. The US has also been trying to find some allied faction inside Libya to work with.

Several European nations have talked up interest in a military operation in Libya, particularly France and Britain, and the expectation is that these nations will all be involved in the attack, though the lack of credible allies is going to make it difficult to present this as mirroring the strategy of the ISIS war in Iraq and Syria.